Provided is a composite separator for gas separation. According to an aspect of the present disclosure, a composite separator for gas separation includes a support and a selective layer disposed on one surface of the support, wherein the support includes a porous polyethylene film, and has a surface roughness of 100 nm or less, a surface median pore diameter of 300 nm or less, and a tensile strength in a machine direction (MD) and a transverse direction (TD) of 10 MPa or more.