A valve operating mechanism for operating at least one valve of an internal combustion engine, includes a camshaft rotatable in synchronism with rotation of the internal combustion engine and having a pair of low- and high-speed cams of different cam profiles, a rocker shaft, and a pair of first and second rocker arms rotatably mounted on the rocker shaft and operable selectively by the low- and high-speed cams for operating the valve according to the cam profiles of the cams. A selective coupling is operatively disposed in and between the first and second rocker arms for interconnecting the first and second rocker arms in high-speed operation of the engine and for disconnecting the first and second rocker arms from each other in low-speed operation of the engine.