I.K.O Kyokusinkaikan was founded by Sosai Mas Oyama. After opening his first dojo in 1954, he launched Oyama Dojo in Tokyo in 1956 where became the base of the Kyokushin Kaikan as an organization.

By 1960, 72 branches had been established throughout Europe and North America due to the vigorous overseas demonstrations.

In 1965, the International Karate Organization (IKO) was officially established as the Tokyo Honbu (headquarter) officially opened.

In 1969, the First All Japan Open Karate Tournament was held at the Tokyo Gymnasium with 7,000 spectators, followed by the First World Open Karate Tournamnet held in 1975. Since then, it had held a number of the remarkable exhibitions including the one at Soviet Embassy in Japan in 1979, another aboard French aircraft carrier Jeanne d'Arc in 1981, and the one in Ukraine by Japanese team in 1990.

After Mas Oyama died in 1994, according to his will, Shokei Matsui was named the successor to the International Karate Organization Kyokushinkaikan and took office as Kancho (Director). In the same year, the 26th All Japan Open Karate Tournament was held, attracting 16,000 spectators. Also, in the following year, the 6th World Open Karate Tournament was held. 168 competitors from 85 countries participated. Spectators numbered 25,000.

In 1996, the knock-down system of the International Karate Organization was introduced worldwide to women's competition and the First Women's World Karate Championship was held in New York with 115 competitors from 23 countries.

In 1997, Mas Oyama Memorial World Weight Category Karate Tournament was held in Tokyo. 80 competitors from all over the world participated spectated by 9,000 people. In the next year, it held World Cup - Team Karate Tournament in Paris, France, with 12 teams representing the 9 regions of the world. It attracted 22,000 spectators and was broadcasted live all over Europe.

The 7th World Open Karate Tournament was held in 1999. 192 competitors from 86 countries participated. Spectators numbering a record 26,000 jammed the Tokyo Taikukan. For the first time in its' history, a non-Japanese fighter took the World Open karate title.

In 2001, besides International One Match Challenge, three great tournaments including the 2nd World Weight Category Championships were held at Osaka Gymnasium, participated by the excellent fighters from 33 countries.

In 2002, The Kyokushin International Challenge was held with an audience of 20,000 on March 23 in Bercy Sports Arena in Paris, France. 32 World-Class athletes from 16 countries competed. Later in the same year, Copa do Mundo - World Cup Team Championships were help at Sao Paulo, Brazil.