Abstract: An improved capacity regulating apparatus for compressors is disclosed. The design comprises a chamber, a sliding member coupled to the chamber and a pair of rotors abutting to and below the sliding member. A piston disposed in the cylinder and the sliding member are coupled to a rod, enabling the sliding member to move axially along a portion of the rod. Two opposite guide slots are provided in opposite sides of the sliding member. A lateral slot is provided inside the sliding member to allow the guide slots in communication with each other; also, an axial slot, extending through a bottom wall of the sliding member, is provided inside the sliding member.