The present invention provides a variable valve mechanism of an internal combustion engine, which includes a rocker arm that is driven by a cam so as to swing to drive a valve, a switching pin that is attached to the rocker arm so as to be shifted between a first position and a second position, a shift device that shifts the switching pin from the first position to the second position, and a return spring that returns the switching pin. In the variable valve mechanism, a drive state of the valve is switched by shifting the switching pin, the rocker arm is formed to have such a dimension that one end of the switching pin is exposed while projecting outward from the rocker arm, and the return spring is externally fitted to the one end of the switching pin so as to be exposed outside the rocker arm.