Abstract: An electrophoresis film support particularly useful for the electrophoretic separation of serum proteins. According to one aspect, the electrophoresis film support comprises a microporous polymer membrane sheet containing therein an additive which is selected from the group consisting of hydroxypropyl cellulose, triphenyl phosphate, tricresyl phosphate and mixtures thereof. According to another aspect the electrophoresis film support comprises a microporous membrane sheet made of a polymer material containing therein an additive which is selected from the group consisting of higher fatty acids having 10 to 27 carbon atoms and mixtures thereof, the additive being contained in an amount, based on the weight of the polymer material, ranging from 10 ppm to 3,000 ppm or the maximum solubility limit of the higher fatty acids in the polymer material.