A method for producing a composition having a disperse phase with small particle size dispersed in a continuous phase and having greater than 20% by volume of a disperse phase. The method comprising a permeation step, wherein a mixture of a continuous phase liquid and a disperse phase liquid simultaneously permeate a circumferential surface of a cylinder, which is partially or wholly composed of a porous membrane. The cylinder having outlets for the composition in the cross sections of both ends of the cylinder. The porous membrane having an average pore size of not smaller than 5 μm at a membrane permeation rate of not lower than 50 m3/m2h. The porous membrane cylinder having a longitudinal effective membrane length, L, the internal diameter of the outlets, d, and the membrane permeation rate, F, which satisfy the relationships disclosed herein of L/d and F.