Provided are polymer particles which can be used at a high flow rate when used as a filler for chromatography, that is, has excellent resistance flow rate appropriate for processing in large quantities, and also has a high binding capacity for target molecules such as proteins when an appropriate ligand is contained in the particles, and a method for producing the polymer particles; specifically, crosslinked polymer particles and a method for producing the crosslinked polymer particles, polysaccharide composite particles and a method for producing the polysaccharide composite particles, a filler for chromatography using the polymer particles, and an adsorbent for antibody purification. Disclosed are: A. a method for producing polysaccharide composite particles, the method including the following steps (1) to (3): (1) a step of preparing a polysaccharide solution, in which two or more kinds of polysaccharides are dissolved in an ionic liquid; (2) a step of preparing a droplet dispersion liquid of the polysaccharide solution, in which liquid droplets of the polysaccharide solution are dispersed in an organic solvent having low compatibility with the ionic liquid; and (3) a coagulation step in which a composite of the polysaccharides are coagulated to obtain the polysaccharide composite particles; and B. a method for producing a crosslinked polymer particle, the method including a step of allowing a polymer dissolved in an ionic liquid, to react with a crosslinking agent while the polymer is subjected to droplet dispersion in an organic solvent having low compatibility with the ionic liquid.