Disclosed is a liposome production process which enables the production of a liposome that has a nano-size particle diameter and a high water-soluble drug encapsulation rate, Specifically disclosed is a process for producing a W1/O/W2 emulsion, which is characterized by comprising the steps of (1) emulsifying an organic solvent (O) that is a volatile organic solvent, an aqueous solvent (W1) and a mixed lipid component (F1) to prepare a W1/O emulsion and (2) dispersing the W1/O emulsion produced in step (1) in an aqueous solvent (W2) using a porous membrane to prepare a W1/O/W2 wherein the surface of the porous membrane has been treated with a hydrophilic component so that the surface has a water contact angle of 0 to 42 DEG inclusive in the air.
