Severo Ochoa (1905-1993), Spanish biochemist, winner of 1959 Nobel Prize in Medicine
George Andrew Olah, (1927- ), 1994 Nobel Prize in Chemistry
Lars Onsager, (1903-1976), physical chemist, winner 1968 Nobel Prize in Chemistry
Hans Christian Ørsted (1777-1851) Danish physicist and chemist
Shimomura Osamu (1928- ) Japanese organic chemist, winner of 2008 Nobel Prize in Chemistry
Wilhelm Ostwald, (1853-1932), winner 1909 Nobel Prize in Chemistry

