A variable compression ratio apparatus for a vehicle engine that is mounted at the engine receiving combustion force of an air-fuel mixture from a piston and rotating a crankshaft mounted between upper and lower cylinder blocks, and that changes compression ratio of the air-fuel mixture by changing a mounting height of the crankshaft according to a driving condition of the engine, may include a bearing having a hollow space eccentric to a center thereof and rotatably mounted between the upper and lower cylinder blocks, the crankshaft being rotatably inserted in the hollow space; and an operating unit provided at the lower cylinder block and controlling a rotational displacement of the bearing.