Margaret Okayo (b. 1977) is a successful marathon runner from Kenya. She has won a number of major marathons.

Amongst her most successful races are the wins at the New York Marathon in 2003 and the Boston Marathon in 2002. On both these courses she holds the course record. She set a new world record over the marathon distance on 4 November 2001 in New York, a record she no longer holds.

Other marathons won by Okayo include the London Marathon in 2004, the marathons of Milan in 2003, San Diego in 2000 and 2001. She is set to represent her native Kenya in the 2004 Summer Olympic Games in Athens, Greece. She spends three months of every year training in Italy.