Microspheres which entrapped PS-K were prepared using Zein as a carrier matrix by a one-step or two-step process in dimethyl sulfoxide-H₂O media. Microspheres prepared by the latter process provided satisfactory recovery and uptake of PS-K. Use of a catalytic amount of dl-camphorsulfonic acid, glutaraldehyde and rapid addition of aqueous solution of polyvinylpyrrolidone into the reaction media are crucial for the preparation of fine and mono-dispersed microspheres. The release rate of PS-K could be controlled by altering the ratio of PS-K to Zein and the conditions of the medium. In the presence of actinase E, drug release was considerably increased to 70-80% after 24 h incubation. Sonication of the aggregated microspheres readily yielded a mono-dispersed preparation with a particle diameter of less than 1 μm, which would be a suitable size for phagocytosis by macrophages.