The first fluid is dispersed in the second fluid to form an emulsion of fine droplets having an average droplet diameter and a droplet diameter distribution equal to or less than the maximum droplet diameter around the average droplet diameter. The solvent is removed from the microdroplets, and the particles change into microspheres having an average particle size and a particle size distribution equal to or less than the maximum particle size centered on the average particle size. The microspheres are subjected to a microfilter having a relatively narrow pore size distribution around the average pore size, and the average pore size is between the average particle size and the maximum particle size. The filtrate of the microfilter contains most of the microspheres that are substantially free of microspheres having a particle size that exceeds the maximum permissible particle size. [Selection diagram] Figure 2第１の流体を第２の流体に分散させ、平均液滴径及び前記平均液滴径の周りに最大液滴径以下の液滴径分布を有する微小液滴のエマルジョンを形成する。前記微小液滴から溶媒が除かれ、平均粒子径及び前記平均粒子径を中心とする最大粒子径以下の粒子径分布を有する微小球に変化する。前記微小球を、平均孔径の周りの比較的狭い孔径分布を有するマイクロフィルターに供して、平均孔径は、前記平均粒子径及び前記最大粒子径の間にある。前記マイクロフィルターの濾液は、最大許容粒子径を超える粒子径を有する微小球が実質的に含まれない前記微小球の大部分を含む。【選択図】図２
