Grace L. MacKnight, 90, a former teacher and retired social secretary who also operated a boarding house here for many years, died of a cerebral vascular accident Thursday at Leewood Nursing Home in Annandale, where she had lived for about three years.

A former Washington resident, she came here in 1923 after her marriage to John D. MacKnight, a Washington butcher. She and her husband operated a boarding house in the DuPont Circle area from the time of their marriage until Mr. MacKnight's death in the early 1960s.

Mrs. MacKnight who was known locally for her penmanship, worked as a social secretary for several Washington hostesses, including Perle Mesta and Marjorie Merriweather Post, in the 1940s. Later, she worked for social organizations such as The Waltz Group of D.C. and the Bachelors and Spinsters Dance Group and arranged coming out parties for local debutantes. She retired at the age of 70.

Mrs. MacKnight was born in Northfield, N.H. She graduated from Emerson College in Boston and taught school in Illinois for two years before her marriage.

She was a member and former officer of the American Philatelic Society.

Survivors include a son, Robert L., of McLean; a stepdaughter, Hazel MacKnight of Mt. Vernon, N.Y.; a sister, Helen Cook of Pawtucket, R.I., two grandchildren and two great-grandchildren.