Duncan McDuffie (September 24,1877-1951) was an architect, real estate developer, and conservationist in San Francisco, California, USA.

McDuffie is best known for designing and developing the St. Francis Wood neighborhood of San Francisco, and the Claremont and Northbrae neighborhoods of Berkeley. McDuffie designed this neighborhoods according to his ideals, making them "residential parks". His neighborhoods have streets that follow the contours of the hills and power lines that run underground.

McDuffie was also a notable conservationist. He was president of the Sierra Club from 1928-1931 and from 1943-1946. He helped create the East Bay Regional Park District in 1934. He won the Pugsley Medal for his service on the California State Parks Commission, where he helped establish the California state park system with the help of his friend, Governor C. C. Young.

McDuffie was also an accomplished climber. He hiked around the Sierra Nevada with Joseph LeConte, Jr. He made first ascents of Mount Abbott and Black Kaweah. The Sierra peak Mount McDuffie is named after him.