A method of manufacturing a composite film, the method including: preparing a coating liquid including a resin and a filler and having a viscosity of from 0.1 Pa·s to 5.0 Pa·s: removing aggregates contained in the coating liquid by making the coating liquid pass through a filter having a minimum pore diameter that is larger than a maximum particle diameter of the aggregates; applying the coating liquid that has been subjected to the aggregate removal on one surface or both surfaces of a porous substrate, to form a coating layer; and solidifying the resin contained in the coating layer, to obtain a composite film including: the porous substrate; and a porous layer that is formed on one surface or both surfaces of the porous substrate and that contains the resin and the filler.