TL;DR
Masutatsu Oyama, founder of Kyokushin Karate, personally chose the Isami K-500 as his go-to gi — and never looked back. It's a 100% cotton, heavyweight, unbleached karate gi handmade in Saitama, Japan, built to survive years of brutal training. It gets harder the more you wear it. It earns its color. If you train Kyokushin seriously, this is your gi. Shop the Isami K-500 Karate Gi →
Mas Oyama's Gi: Isami K-500 Karate Gi (Kyokushin Guide)
Some gis are made to look good on the shelf. The Isami K-500 karate gi was made to survive a Kyokushin fighter. There's a difference — and Sosai Mas Oyama knew it.
What Gi Did Mas Oyama Wear?
Masutatsu Oyama, founder of Kyokushin Karate and one of the most demanding martial artists in history, wore the Isami K-500. He didn't wear it because it was new or trendy. He wore it because it was the most durable, comfortable gi he had ever trained in — his words.
The connection runs deep. Isami's president at the time, Mr. Shigeyuki Iso, was a personal acquaintance of Sosai Oyama. That relationship led Oyama to first try Isami's lineup, starting with the unbleached classic — the K-400 — before the K-500 came out and changed everything.
When Isami released the K-500 as an upgrade, Oyama adopted it immediately. In his own words: it was the most long-lasting and easy-to-wear karate gi he had ever tried. That's the entire product review, straight from the founder of Kyokushin.
Get the Mas Oyama Isami gi here →
Why the Isami K-500 Became the Standard in Kyokushin
Once the Isami K-500 karate gi became Sosai's daily training uniform, Isami supplied him with multiple sets per year. He would wear each one through training, then pass it to a Deshi — a personal student — as a gift.
That's how the gi's reputation spread across Japan. Kyokushin practitioners saw what their seniors were wearing. They understood what it meant. An authentic kyokushin gi passed down from Sosai himself carried weight that no marketing campaign could match.
Today, decades later, serious Kyokushin practitioners in Japan still train in the K-500 exclusively. It's not nostalgia. It's that the gi simply performs. The ivory unbleached canvas gets tougher with every wash and harder with every session — a physical record of your mat time.
ChokeSports.com has been Isami's official international partner since 2006. Every K-500 we ship is the same gi made in the same factory in Saitama, Japan, with the same handcrafted construction Sosai trained in.
Shop the authentic Kyokushin gi by Isami →
What Makes a Kyokushin Gi Different?
Not all karate gis are made equal — and Kyokushin has specific demands that most gis simply can't meet. Here's what separates a real kyokushin karate gi from a standard uniform:
- Weight: Kyokushin gis are heavier — typically 12 oz canvas on the jacket. That thickness resists ripping during takedowns, grabs, and full-contact exchanges.
- Cut: The jacket is shorter and tighter than traditional gis. Full contact karate demands free hip rotation and fast kicks — a baggy gi gets in the way.
- Material: 100% cotton canvas jacket, 100% cotton twill pants. No blends, no synthetics. Cotton absorbs sweat, wicks it away from skin, and holds its structure through hundreds of washes.
- Reinforced stitching: High-stress points — collar, lapel, sleeve joins — are double or triple stitched. A cheap gi tears here first.
- Unbleached fabric: Ivory/natural color isn't just tradition. Unbleached cotton retains more of its original fiber strength. It wears in, not out.
A lightweight karate gi designed for sport karate or Shotokan kata won't survive Kyokushin randori. Kyokushin gi requirements exist for a reason: the training is harder, the contact is real, and the gear must match.
The Isami K-500 meets every one of those requirements. It was designed for this.
Is the Isami K-500 Worth It?
Short answer: yes — if you train Kyokushin seriously.
What you get with the Isami K-500:
- Handmade in Saitama, Japan — same factory, same craftsmen, same quality since 1932
- 100% cotton canvas jacket (heavyweight) + 100% cotton twill pants
- Full contact Kyokushin cut — optimized for kicks, not aesthetics
- Reinforced stitch lines that will not break under real training pressure
- Unbleached ivory color that ages into white — exactly as Sosai described
- Pre-order available for all sizes, with production updates direct from Isami
Who it's for: Any serious Kyokushin practitioner or full contact competitor who wants the Japan-made, maximum-durability version — the exact gi Sosai chose.
"Train hard, and train until the dogi color becomes white." — Sosai Mas Oyama
That quote isn't just inspiration. It's a product description. The K-500 starts ivory and turns white through sweat, repetition, and time. Your training history is written into the fabric.
Get your Isami K-500 karate gi at ChokeSports →
Isami K-500 vs K-400: Which Should You Choose?
Both gis share Isami's full contact DNA and unbleached cotton construction. The difference comes down to origin, fabric weight, and feel.
| Isami K-500 | Isami K-400 | |
|---|---|---|
| Origin | Handmade in Japan | Isami full contact line |
| Fabric | Harder, thicker canvas | Standard full contact cotton |
| Feel | Stiffer — breaks in over time | Ready to train from day one |
| Best for | Competitors, dedicated practitioners | Advanced fighters, daily training |
| Legacy | Mas Oyama's personal gi | Isami's classic full contact gi |
| Durability | Extreme — 10+ years | High — built for serious training |
Choose the K-500 if you want the Japan-made original — harder fabric, thicker canvas, and the same construction Mas Oyama trained in for decades.
Choose the lighter kyokushin gi option — the Isami K-400 if you want Isami's proven full contact quality in a slightly lighter, more flexible build. It's still a serious gi built for serious fighters — just a different weight class.
Isami K-500 Sizing Guide
The K-500 runs true to Isami's Japanese sizing chart. A few things to know before ordering:
- Size up if you're between sizes. The canvas shrinks slightly after the first wash.
- Jacket and pants can be ordered separately, or in mixed sizes if you're longer in the torso than the legs.
- Pre-order sizes ship in approximately 2–3 months. Production is handmade and cannot be expedited.
- Contact ChokeSports directly if your measurements fall between sizes — the team has been fitting fighters globally since 2006.
Frequently Asked Questions
What gi did Mas Oyama wear?
Masutatsu Oyama wore the Isami K-500 — a heavyweight, unbleached, full contact karate gi made in Japan. He chose it for its durability and comfort, and described it as the best gi he had ever worn.
What makes a Kyokushin gi different from other karate gis?
Kyokushin gis are heavier, stiffer, and cut shorter than standard gis. They use heavyweight cotton canvas, reinforced stitching, and a full contact cut designed for kicking range and grip resistance — demands that standard gis aren't built to meet.
Why are Kyokushin gis heavier than other styles?
Full contact Kyokushin involves real grabs, throws, and heavy striking. A lightweight gi tears, bunches, and loses shape under that stress. Heavyweight canvas holds its form, resists tearing, and actually gets tougher over time.
How does the Isami K-500 compare to the K-400?
Both are full contact, unbleached cotton gis built for advanced practitioners. The K-500 is made in Japan using a harder, thicker canvas — it's the heavier, more demanding build, and the one Mas Oyama wore. The K-400 is Isami's classic full contact gi: same serious pedigree, slightly lighter fabric, ready to perform from session one.
Is the Isami K-500 good for beginners?
It can be used by beginners with guidance, but expect a break-in period — the heavy canvas is stiff at first. If you want immediate comfort while still training in authentic Isami gear, the Isami K-400 is a strong starting point.
Where can I buy an authentic Isami K-500?
ChokeSports.com is Isami's official international partner since 2006. Every K-500 ships direct from Isami's factory in Saitama, Japan. Order your Isami K-500 here →
Get Mas Oyama's Gi. Earn the White.
The Isami K-500 isn't a fashion choice. It's a commitment. It's the mas oyama karate gi worn by the man who built Kyokushin from the ground up — and passed it to his students as a symbol of serious training.
Every fighter who trains in it walks the same path. Buy once. Train forever. Let the gi turn white.
→ Shop the Isami K-500 Karate Gi at ChokeSports.com
Isami's Official International Partner Since 2006. Handmade in Saitama, Japan.
