A motorcycle cruise control system intended for cooperation with a rotary throttle grip of a motorcycle, comprises a clamping device with a stationary clamping part and a movable clamping part which is movable between a clamping position for clamping the throttle grip and maintaining it in a desired rotary position, and a release position allowing a rotation of the throttle grip, an operating mechanism for moving the movable clamping part between its clamping and release positions and a holding arrangement for holding the clamping device substantially stationary with respect to the motorcycle. The operating mechanism comprises an eccentric mechanism with a first arm and a second arm of which respective first ends are pivotably connected to the stationary clamping part and movable clamping part, respectively, and of which the second ends are pivotably connected to each other.