Mariko Ōhara(大原まり子,Ōhara Mariko?, born 1959 in Osaka, Japan) is a Japanese science fiction writer. In her teens, she wrote Kirk/Spock fan fiction. She graduated from Seisin University and her writing career began in 1980.
In 1991 her Haiburiddo Chairudo (Hybrid Child) won the Seiun Award for Japanese novel. Then in 1995 she won the 15th Nihon SF Taisho Award for Senso-wo Enjita Kamigamitachi (Gods who Bandied War). From 1997 to 1999 she was on the jury for the Taisho awards. At present she is a science fiction reviewer for Asahi Shimbun and a member of the Japanese Writers' Association. In addition to this she was president of the Science Fiction and Fantasy Writers of Japan from September 1999 to September 2001.