This method for producing extended release particles (1) comprises: an oil phase component preparation step wherein an oil phase component containing a hydrophobic slurry is prepared by dispersing an antibiotically active compound, which is hydrophobic and substantially insoluble in a hydrophobic polymerizable vinyl monomer, in a hydrophobic polymerizable vinyl monomer in the absence of a solvent a water dispersion step wherein a water dispersion liquid is prepared by dispersing the hydrophobic slurry in water and a polymerization step wherein the polymerizable vinyl monomer is subjected to suspension polymerization, thereby producing a polymer.
