Leôncio Basbaum (1907–1969) was a Brazilian Marxist historian.
Basbaum, the child of Jewish immigrants from Ukraine, was born and raised in the state of Pernambuco. He qualified as a medical doctor in Rio de Janeiro in 1929. Basbaum become involved in the Brazilian Communist Party following his graduation and dedicated the rest of his life to the cause.
Basbaum's four-volume História Sincera da República is widely respected as a seminal work on Brazilian history from a Marxist perspective, in virtue of which Busbaum is considered one of Brazil's most important historians.