Sigma Phi Omega was founded at the University of Southern California in 1949, and is the oldest Asian-American sorority at USC and 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 alumni 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.)

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 the treatment of Asian American, specifically Japanese Americans, by the campus.

Membership consisted primilary those of Japanese descent in the beginning, although it was open in membership. The new member program was implemented in the mid-1950's.