There is provided a method of producing a composition having a continuous phase and a disperse phase dispersed finely with low polydispersity in the continuous phase, with high production efficiency.The composition is produced by the production method including the steps of: (A) passing the swirling flow of the continuous phase liquid into a cylindrical body the circumferential surface of which is either in part or entirely formed by a porous membrane, (B1) supplying the disperse phase fluid to the swirling flow via the porous membrane to form the particles of the disperse phase on the porous membrane, and (B2) detaching the disperse phase particles formed on the porous membrane by the shear force of the swirling flow. The cylindrical body preferably has an inlet for the continuous phase liquid on the circumferential surface of the cylindrical body in the vicinity of one end of the cylindrical body and an inlet tube which extends from the inlet in the substantially vertical direction to the axis of the cylindrical body and the tangential direction to the cylindrical body. The step (A) is preferably carried out by use of the inlet tube to flow the continuous phase liquid in from the substantially vertical direction to the axis of the cylindrical body and the tangential direction to the inner wall surface of the cylindrical body.
