Organic-inorganic hybrid particles of nanosilica encapsulated by Poly (methyl methacrylate-co-butyl acrylate) were synthesized by a soap-free seeded emulsion polymerization. The nanosilica was initially treated by a silane coupling agent bearing unsaturated carbon double bond to increase its hydrophobicity and enhance its ability to take part in free radical polymerization. Two ionic comonomers including sodium salt of styrene sulfonic acid (NaSS) and potassium methacrylate (KMAA) were used simultaneously to stabilize the nanoparticles and create ionic charge groups on their surface. The prepared samples were characterized by different methods. The X-ray photoelectron spectroscopy (XPS) and energy dispersive X-Ray analysis (EDX) results confirmed the simultaneous presence of both ionic co-monomers on the surface of the nanoparticles; however, their population on the surface was not proportional to their concentrations in the feed. The burial of the KMAA was more significant than that of NaSS and the NaSS reduced the average particle size more sharply than KMAA. Thermogravimetric analysis (TGA) showed that the efficiency of encapsulation was around 100% and no free polyelectrolyte chains were synthesized during the course of the polymerization. Transmission electron microscopy (TEM) showed an organic/inorganic hybrid structure for the prepared encapsulated nanosilica. (C) 2018 Elsevier B.V. All rights reserved.