James Fraser Mustard, C.C., O.Ont., M.D., LL.D., F.R.S.C., (born 1927) is a Canadian physician and scientist.

Born in Toronto, Ontario, he attended Whitney Public School and the University of Toronto Schools graduating in 1946. He received a MD from the University of Toronto in 1953. He interned at the Toronto General Hospital and spent two years of postgraduate study at the Department of Medicine, Cambridge University, where he earned his Ph.D.

Upon returning to Canada, he was a senior intern at Sunnybrook Hospital and then a senior research associate with the Department of Veterans Affairs and a fellow in the Department of Medicine, University of Toronto. In 1958, Mustard received a Medal of the Royal College of Physicians of Canada for an essay entitled, "A Study of the Relationship Between Lipids, Blood Coagulation and Atherosclerosis."

From 1960 to 1961, he was a research associate with the National Heart Foundation of Canada, and from 1962 to 1963 a research associate with the Department of Medicine, University of Toronto and a senior research associate with the Canadian Heart Foundation. He became a Fellow of the Royal College of Physicians and Surgeons of Canada in 1965.

In 1966, he was a founding member of the McMaster University Faculty of Medicine and the first chairman of the Department of Pathology. In 1972, he became Dean and Vice-President of the Faculty of Health Sciences. In 1982 he became president of the Canadian Institute of Advanced Research .

He is a Fellow of the Royal Society of Canada and the winner of the 1993 Sir John William Dawson Medal. In 1985 he was made an Officer of the Order of Canada and was promoted to Companion in 1993. He is a receipent of the Order of Ontario.

In 2003 he was inducted into the Canadian Medical Hall of Fame.

He is the Past Chairman of Ballard Power Systems.

Mustard has been the recipient of fifteen Honorary Degrees.