Poly(n-octadecyl methacrylate-co-2-hydroxyethyl methacrylate) [poly(OMA-co-HEMA)] block copolymers were synthesized by free radical polymerization from n-octadecyl methacrylate (OMA) and 2-hydroxyethyl methacrylate (HEMA) and these copolymers have been assessed as stabilizer in the preparation of polycaprolactone (PCL) microspheres using non-aqueous dispersion polymerization. The copolymer poly(OMA-co-HEMA) has been used as in situ stabilizer in the preparation of PCL microspheres at 80 A degrees C. Spherical PCL microspheres are found to be well dispersed and uniform in size which demonstrated the efficient of OMA: HEMA copolymer as replacement of preformed stabilizer in synthesis of PCL microspheres. The factors affecting in the preparation of PCL microspheres such as polymer molecular weights and molecular weight distribution, particle size and distribution and morphology were studied. The synthesized poly(OMA-co-HEMA) copolymer used as in situ stabilizer is characterized by FT-IR, NMR, XRD and GPC techniques. The morphology and particle sizes of the prepared microspheres are observed by field emission scanning electron microscope.