A novel macromonomer of vinyl-terminated bifunctional polyurethane was synthesized and applied to the dispersion polymerization of MMA in ethanol. The existence of the vinyl terminal groups and the grafted macromonomer with PMMA was verified using 1H NMR and 13C NMR. The stable and monodisperse PMMA microspheres having a weight-average diameter of 5.09 microm and a good uniformity of 1.01 were obtained with 20 wt% polyurethane macromonomer. The molecular weight increased, but the size of the synthesized PMMA microspheres decreased with the macromonomer concentration since the macromonomer acts as a reactive stabilizer in dispersion polymerization. Furthermore, the molecular weight of the PMMA prepared by the use of the macromonomer was approximately twofold higher than that prepared by a conventional stabilizer, poly(N-vinylpyrrolidone). The higher molecular weight is thought to originate from the grafting and a possibly slight crosslinking of PMMA molecules due to the bifunctional reactive groups at the ends of macromonomer chains.