Leo and Tobey partied aboard a yacht in St. Tropez with a few hot chicks ... days after Leo raised about $40 million for his foundation benefiting wildlife protection.

Leo did some quick work ... pouncing on a brunette who apparently needed some sorta mouth-to-mouth treatment. Tobey perfected his role as wingman chatting up a couple bikini-clad beauties.

Gotta give it up for Tobey though ... taking 2 for the team!