An electro-optical composite connector includes a receptacle connector including a receptacle housing to be mounted on a first board, a receptacle shell for covering the receptacle housing, and a receptacle terminal arranged on the receptacle housing; and a plug connector including a plug housing for holding an optical fiber, a plug shell for covering the plug housing, and an optical module to be connected to the optical fiber. The optical module includes a second board; a light receiving/emitting element mounted on one surface of the second board; at least one of a plug terminal and a land mounted on the one surface of the second board for transmitting a signal relative to the receptacle terminal; and a grounding surface formed on the other surface of the second board opposite to the one surface. The grounding surface is electrically connected to an inner wall of the plug shell.