Abstract: With the ultrasonic assistance, octamethylcyclotetrasiloxane(D4)and a little of silane coupling agent γ-(2, 3-epoxypropoxy) propyltrimethoxysilane (KH560) were sufficiently mixed with silica sol and the in-situ ring-opening polymerization of D4 and co-condensation with KH560 on the surface of silica nanoparticles, catalyzed by dodecylbenzene sulfonic acid (DBSA), were enhanced as well. The polydimethylsiloxane (PDMS) modified silica was obtained. The PDMS-modified silica sol was dispersed in the mixed monomers of methylmethacrylate (MMA) and butylmethacrylate (BA). Then miniemulsion polymerizations of the acrylate monomers containing PDMS-modified silica sol were carried out, with PDMS as hydrophobe to inhibit the Ostwald ripening of the monomer droplets and neutralized DBSA as emulsifier, both preexisted in the PDMS-modified silica sol. The SiO₂/polyacrylates composite latex was obtained via miniemulsion polymerization. FTIR, TGA, TEM, Malvern Nanosizer and water contact angle tests were utilized to characterize the modified silica and the composite latex. The results show that silica is grafted and encapsulated by PDMS and KH560 with chemical bonds and is well dispersed in monomers, and the generated PDMS improves the hydrophobicity of the film of nanocomposite latex. The average size of nanocomposite particles with a (multi)core-shell structures is 98 nm when the silica mass fraction is 3% of the monomers.