Sigma Phi Omega was founded at the University of Southern California in 1949, and is the oldest Asian-American sorority at USC and the third oldest in the United States. It was originally established as a social organization for Japanese and Japanese-American women at USC. There was much anti-Asian sentiment left behind by World War II, which had ended in 1945. As one alumna said, "At that time it was understood that Asian women could not become members of a sorority. It has since changed. Thank goodness."

In its early beginnings, the founding mothers of Sigma Phi Omega were invited by Chi Alpha Delta, an Asian-American sorority from UCLA, to become one of their chapters. (Chi Alpha Delta had been chartered in 1928 at UCLA, but was rendered inactive between 1942 and 1945 because the majority of its members were unable to attend UCLA due to World War II. After the end of the war, the sorority was reorganized in 1946.)

	Founding Mothers Miki Haga Joyce Ishibashi Tawa Ida Kado Watanabe Kazuko Kay Matsumoto Helen Morita Matunaga Mitzi Okamoto Cherry Okimoto* Thelma Sasada Akiko Sato Miyamoto Edna Tanaka Helen Taniguchi Wakamatsu Miki Tanimoto* Dottie Uno Julia Uriu* Grace Wada Iino* Betty Wakamatsu Chiyoe Yata Oki
* Indicates the passing of the individual

However, our founding mothers decided to start their own organization. The Greek letters were chosen at random and were not used by any other existing fraternities or sororities at that time. Although we did not originate as a sorority, one could speculate that the choosing of Greek letters was a public way of voicing a dissatisfactory opinion about treatment of Asian Americans, specifically Japanese Americans, by the campus and Greek organizations.

Membership was primarily those of Japanese descent in the beginning, although it was open in membership. The pledge program was implemented in the mid-1950's.

Today, there are seven other chapters located in both California and Texas.