A process for production of a composite porous film wherein a porous support, of which both sides have been coated with a solution (dope) of an organic polymer compound in a water-soluble organic solvent to form a coated film, is passed through an air gap step and conveyed into a coagulating bath comprising water or a mixture of water with the same solvent as the organic solvent, and is then immersed in the coagulating bath so that the coated film on both surfaces of the porous support directly contact the coagulating bath for coagulation, and is then washed and dried. This production process is suitable for production of non-aqueous secondary battery separators, and yields non-aqueous secondary battery separators with good handling properties and at low cost, whereby the ion permeability, adhesion with electrodes and electrolyte solution retention can be strictly controlled.