A series of monodispersed polyaminopropylmethylsilsesquioxane (PAMSQ) nanospheres were fabricated via emulsion polymerization of Methyl triethoxysilane (MTES) in aqueous solution and sodium hydroxyl was used as catalyst, γ-aminopropyl triethoxysilane (KH550) as a modifier, sodium dodecyl sulfonate/fatty alcohol-polyoxyethylene ether (SDS/AEO-9) as mixed emulsifiers. Structure, thermal stability, particl size distribution, microscopic morphology of PAMSQ were investigated by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), Thermogravimetric analyzer (TGA), Dynamic Light Scattering (DLS), Field emission scanning electron microscopy (FESEM) and Atomic force microscopy (AFM). Results indicate that a series of PAMSQ nanospheres with an average particle size of about 30~150 nm could be prepared while the doses of NaOH were controlled as 0.018~0.08 wt%. Meanwhile the average particle size of the monodispersely and regularly spherical PAMSQ increased with augment of the NaOH dose. PAMSQ possessed the favorable thermal stability.