To provide a novel technique of structural control intended for the liquid-liquid phase separation membrane of polyethylene fine porous membranes.

In the process for the preparation of polyethylene fine porous membranes by kneading a mixture of a polyethylene and two or more plasticizers at a temperature not-lower-than the melting point of the polyethylene, cooling and solidifying the kneaded mass at a temperature of not higher than the crystallization temperature of the polyethylene and then, removing the plasticizers, are used such not less than two plasticizers that the phase separation temperature of the kneaded mass can exhibit nonlinearity to the weight ratio of each component of the plasticizers.