The present invention provides for a method of producing an integral multilayered porous membrane by simultaneously co-casting a plurality of polymer solutions onto a support to form a multilayered liquid sheet and immersing the sheet into a liquid coagulation bath to effect phase separation and form a porous membrane. The support can be a temporary support or form an integrated support for the membrane. The plurality of layers may be of the same polymer or different, same concentration or viscosity or different and may be subjected to the same processing conditions or different ones to form unique structures.