Alceste de Ambris (1874-1934) was an Italian anarcho-syndicalist.

With Gabriele D'Annunzio, he coauthored the Carta del Carnaro, a Constitution of Fiume. De Ambris provided the legal and political framework for the document while D'Annunzio used his skills as a poet to make the document more impressive. De Ambris was the leader of a group of Italian seamen who had mutined and then given their vessel to the service of D'Annunzio.