A Senatus consultum ultimum ("Ultimate decree of the Senate"), or more properly, senatus consultum de re publica defendenda ("Decree of the Senate on defending the Republic") was a decree of the Roman Senate during the late Roman Republic passed in times of emergency. It was adopted after the end of the Second Punic War as a replacement for the dictatorship, essentially giving the magistrates semi-dictatorial powers to preserve the State.

It was first passed during the rise to power of the younger of the Gracchi in 121 BC and subsequently during the Catiline Conspiracy in 63, Clodius' desecration of the rites of Bona Dea the following year, and finally when Julius Caesar crossed the Rubicon in 49.