Highly monodisperse poly(methyl methacrylate)(PMMA) microparticles crosslinked with urethane acrylates containing carboxylic groups were produced by dispersion polymerization in methanol solution. Different from conventional crosslinkers, the urethane acrylate employed as a crosslinker showed an excellent effect on maintaining the monodispersity of PMMA microparticles even in the moderate crosslinker concentration (to about 10 wt%). This was believed that the urethane acrylate helped forming the monomer-swellable surface of primary particles, because of its structurally long tetramethylene oxide groups in its molecule. However, at high concentration and low molecular weight of the urethane acrylate, bimodal distributions were observed, which was attributed to the serious increase of the crosslinking density.