Ioan I. Cantacuzino (Romanian pronunciation: [iˈo̯aŋ kantakuziˈno]; also Ion Cantacuzino; 25 November 1863 – 14 January 1934) was a renowned Romanian physician and bacteriologist, a professor at the School of Medicine and Pharmacy of the University of Bucharest, and a titular member of the Romanian Academy. He established the fields of microbiology and experimental medicine in Romania, and founded the .