The present invention relates to a variable apparatus for separating oil from blow-by gas in an engine. More particularly, the variable apparatus of the present invention is installed in a baffle compartment of a cylinder head cover of the engine, and includes a partition wall (10), a cover (20) and an elastic member (30) that elastically supports the cover (20), thus separating oil from blow-by gas generated in the engine. The variable apparatus having the above-mentioned construction actively responds to the flow speed of the blow-by gas, thus markedly enhancing the ability to separate oil from blow-by gas even when the engine is operating at high speed.