A mechanical rod rotator assembly comprising a mechanical rod rotator and an actuating mechanism for a mechanical pumping rod rotator, wherein the mechanism comprises a connecting arm and a guide member that slidably embraces the pumping rod, in order to allow a pivoting lever that is in connection with said connecting arm, to interact with the internal mechanism of the rod rotator to gradually rotate the pumping rod and thus avoid impartial wear caused by the constant up and down reciprocating movement of the same within the well, being in turn that the mechanism of the invention does not require special tools for its assembly and installation.