A process for preparing a composite membrane comprising a porous support layer and a discriminating layer, comprising the steps of: (a) providing a porous support layer; (b) incorporating an inert liquid into the pores of the support layer; (c) applying a curable composition to the support layer; and (d) curing the composition, thereby forming the discriminating layer on the porous support. The process is particularly useful for preparing gas separation composite membranes.