Miyoko Watai (渡井 美代子, Watai Miyoko, born January 8, 1945) is a Japanese women's chess champion, and the general secretary of the Japan Chess Association. She is a Woman International Master. She lives in the old Kamata ward, which is now part of Ōta, Tokyo.
In 1973 she met then world chess champion Bobby Fischer, and visited him several times for the next three decades. Starting in 2000 they reportedly lived together in a de facto marriage at her home. After Bobby Fischer's detention on July 13, 2004 for trying to travel with a revoked U.S. passport, she campaigned for his release.
They were reportedly married in August 2004. According to an attorney representing a competing claim to Fischer's estate, the Supreme Court of Iceland ruled in December 2009 that Watai's claim of marriage to Fischer was invalidated because of her failure to present the original of their alleged marriage certificate. However, on March 3, 2011, a district court in Iceland ruled that Miyoko Watai, as Fischer's widow and heir, was entitled to inherit his estate.