|Born||April 11, 1972
Muroran, Hokkaidō, Japan
|2002-||Japan Football League||Referee|
Her first international tournament was the 2002 FIFA U-19 Women's World Championship in which she officiated two games including the third place play-off. Following her performance in the 2004 FIFA U-19 Women's World Championship, in which she refereed a Quarter final match, Oiwa was promoted to the Japan Football League.
She became the first female referee to officiate in the 84th Nationwide Highschool soccer championship conference on January 22, 2006, and then refereed the final at the 2006 AFC Women's Championship.Selected by FIFA to officiate in the 2007 FIFA Women's World Cup in China, she refereed two games and was fourth official in the Final between Germany and Brazil.
- "OIWA Mayumi". FIFA Women's World Cup China 2007 - Referees. FIFA. Retrieved 2007-10-03.
- "Women's World Cup Referees List". Soccer. CBS Sports. 2007-06-21. Retrieved 2007-09-29.
- "Match Report - Germany - Brazil". FIFA Women's World Cup China 2007. FIFA. Archived from the original on 2007-10-23. Retrieved 2007-10-03.