A variable valve mechanism includes a camshaft and a cam unit. Internal spline teeth provided at an inner periphery of a sleeve of the cam unit are in mesh with external spline teeth provided at an outer periphery of the camshaft. An engaging portion is provided at one of the inner periphery of the sleeve and the outer periphery of the camshaft, and is configured to retractably project toward the other one of the inner periphery of the sleeve and the outer periphery of the camshaft. A latching portion is provided at the other one of the inner periphery of the sleeve and the outer periphery of the camshaft. The sleeve has a through-hole that is provided at the same position in a circumferential direction as the engaging portion to supply the inner periphery of the sleeve with lubricating oil.