A novel crosslinkable macromonomer of vinyl terminated difunctional polyurethane was synthesized and applied to the dispersion polymerization of MMA in ethanol. The monodisperse crosslinked PMMA microspheres having the size (D_w) of 5.09 μm and good uniformity of 1.01 were obtained with 20 wt% polyurethane macromonomer. Due to the crosslinked structure of the microspheres, the higher molecular weights and much enhanced thermal stability of the PMMA was obtained compared to the one prepared using the noncrosslinkable conventional stabilizer, PVP. These results indicate that the macromonomer acts as a stabilizer as well as an effective crosslinking agent and that the monodisperse crosslinked microspheres could be prepared using this type of macromonomer without altering the surface smoothness and particle shape.