Elizabeth Thayer Vincent, 80, a former Washington interior decorator and widow of John Carter Vincent, one of the State Department's "old China hand," died of cancer Nov. 24 at her home in Cambridge, Mass.

Mrs. Vincent had accompanied her husband to diplomatic posts in China, Switzerland and Morocco. She had lived in Washington in the mid-1930s and mid-1940s, between foreign assignments, where she was self-employed as an interior decorator in Georgetown.

After her husband's retirement from the Foreign Service in the early 1950s, the family moved to Cambridge. Mr. Vincent, who died in 1972, came to be recognized in the years following his retirement as one of the principal victims of the McCarthy era and hysteria about the Communist takeover of China.

Mrs. Vincent was born and reared in Chicago. During the 1920s, she lived in New York City and then traveled in Europe and China. While in Peking, she met Mr. Vincent, and they were married there in 1931.

Survivors include two children, John Carter Vincent Jr., of Boston, and Sheila V. Cox, of Los Angeles, and six grandchildren.

The family suggests that expressions of sympathy be in the form of conttibutions to the American Cancer Society or the Civil Liberties Union of Massachusetts.