Abstract: The carboxylic waterborne polyurethane was synthesized with isophorone diisocyanate(IPDI), polyether glycol(N210) and 2,2-bis(hydroxymethyl) propionic acid(DMPA) as the major materials, and terminated by C=C from β-hydroxyethyl methacrylate(HEMA). SiO₂-PMMA composite microspheres were prepared with different types of initiators by double in situ miniemulsion polymerization, in which the waterborne polyurethane was used as a polymerizable surfactant. The prepared products were characterized by TEM, FTIR and TGA, respectively. The results indicate that morphologies of the SiO₂-PMMA composite microsphere prepared by waterborne polyurethane surfactant(PUS) are different from those prepared by conventional micromolecule surfactants. The type of initiators affects significantly on the morphologies of the SiO₂-PMMA.