Membrane technology has been used in separation processes such as wastewater treatment, desalination, and hemolysis. However, in proccess of the non-solvent-induced phase separation (NIPS) which is the most widely adopted method for fabricating porous polymer membranes, using toxic organic solvents is a critical problem for environmental aspect. To resolve this problem, the aqueous phase separation (APS) has received attention, which produces polymeric membranes without using the organic solvent. In this review, we provide principle and process of APS. The ratio of monomers, pH and salt concentration in aqueous solution, viscosity of casting solutions, and concentration of cross-linkers can leverage the structures of membranes.