The mud guard system for a chain of a motorcycle in which a drive chain is made to run on both a front sprocket connected to an engine and a sprocket connected to a rear wheel at the trailing end of a rear fork, comprises a mud guard member having a cylindrical shape for allowing the chain to run therethrough and disposed at one side of the rear wheel and a link or another connecting member for coupling the mud guard member floatingly to the rear fork so that the mud guard member can move in the longitudinal direction of the chain.