A variable compression ratio apparatus may include an external piston, a piston pin mounted in the external piston and a connecting rod, including an internal piston including a slot and sliding in an interior circumference of the external piston, wherein the piston pin passes through the internal piston and the external piston, a latching pin passing through the piston pin and selectively sliding therein, variable sliders disposed to selectively contact one of both ends of the latching pin, at both sides thereof to push the one of the both ends to the opposite side, and a support plate slidably supporting the variable sliders such that the variable sliders reciprocate perpendicular to length direction of the latching pin, wherein one end of a connecting arm selectively rotating may be connected to the variable slider and a sliding direction of the variable sliders may be controlled by rotation of the connecting arm.