Reginald Heber Fitz (b. 1843, Chelsea, Massachusetts – 1913) was an American physician.
He graduated in 1864 (M.D., 1868) from Harvard University, where, after studying in Vienna, Berlin, and Paris, he was instructor in pathological anatomy in 1870–1873, assistant professor in 1873–1878, and professor from 1878 to 1908. In the latter year he became professor emeritus.
He also served as physician to the Boston Dispensary in 1871–1882 and to the Massachusetts General Hospital from 1887 to 1908. In 1894 he was president of the Association of American Physicians. Besides his contributions to medical journals, he is joint author with Horatio C. Wood of The Practice of Medicine (1897).