The invention offers a microporous modified-polytetrafluoroethylene membrane that is a microporous membrane having a significantly small pore diameter and narrow pore-diameter distribution and that can remove microscopic foreign particles at high efficiency when used as a filtration membrane. A microporous modified-polytetrafluoroethylene membrane that is a microporous membrane produced by the steps of producing a copolymer of hexafluoropropylene or perfluoroalkyl ether and tetrafluoroethylene having the number of moles not less than 50 times that of the hexafluoropropylene or perfluoroalkyl ether, forming the copolymer into the shape of a membrane, heating the membrane to the melting point of the copolymer or above to bake the copolymer, cooling the obtained baked product, and stretching the baked product and that has a mean flow pore diameter of 30 nm or less; a porous-modified-polytetrafluoroethylene-membrane composite that incorporates the microporous membrane and a production process of the composite; and a separation membrane element incorporating the porous-modified-polytetrafluoroethylene-membrane composite.