Controlled release particles are obtained by dissolving a hydrophobic antibiotic compound in a hydrophobic polymerizable vinyl monomer without the presence of a solvent, thereby preparing a hydrophobic solution, the hydrophobic antibiotic compound having a melting point of 100° C. or less, a polar term δp,compound of 2 to 8 [(J/cm3)1/2] of a solubility parameter (δ) and a hydrogen bonding term δh,compound of 5.5 to 9.5[(J/cm3)1/2] of the solubility parameter (δ), the solubility parameter (δ) defined by Hansen and calculated by van Klevelen and Hoftyzer method dispersing the hydrophobic solution in water and polymerizing the polymerizable vinyl monomer in the presence of an oil-soluble initiator by radical polymerization, thereby producing a polymer having a polar term δp,polymer of 5 to 7[(J/cm3)1/2] and a hydrogen bonding term δh,polymer of 8 to 10 [(J/cm3)1/2] of the solubility parameter (δ).
