UFC 23: Ultimate Japan 2 was a mixed martial arts event held by the Ultimate Fighting Championship on November 19, 1999 at Tokyo Bay NK Hall in Tokyo, Japan.

UFC 23 was headlined by a Heavyweight Championship Title bout between Kevin Randleman and Pete Williams, held to determine the champion after Bas Rutten's retirement.

The event also featured a four-man "Japanese" tournament, held to crown the first ever UFC Japan Champion.

SEG originally intended UFC Japan to be a separate company, run by local promoters, but due to mounting financial problems, a lack of cooperation from Japanese promoters, and the rise of the popular PRIDE and K-1 organizations, the idea was scrapped following UFC 25: Ultimate Japan 3.

Bas Rutten announced at UFC 23 that he dropped his heavyweight championship title so he could drop down to middleweight to bring Frank Shamrock out of retirement to fight for the middleweight championship.