Oscar Jenckes Rathbun (March 12, 1832 – February 1, 1892) was an American businessman and politician, serving as the Lieutenant Governor of Rhode Island from 1883 to 1885.
He attended Worcester High School in Massachusetts and the Clinton Liberal Institute in New York.
In 1882, he was elected lieutenant governor of Rhode Island alongside Augustus O. Bourn.
After his time as lieutenant governor, he retired from politics in order to devote himself more to his business.
In the afternoon of the same day he felt unwell and wanted to return to Woonsocket.