A variable valve mechanism for an internal combustion engine includes a control shaft and a cam. The control shaft is configured to change a maximum lift amount of an engine valve according to displacement of the control shaft. The cam is configured to displace the control shaft in the axial direction due to rotation of the cam. The cam surface includes change zones and retention zones. Respective lengths of the retention zones in a rotation direction of the cam is set such that respective length of the retention zones in the rotation direction increases as the maximum lift amount retained by the retention zones increases.