Hyperbranched polyethylenimine (PEI)-functionalized mesoporous silica (MCM@PEI) was synthesizedand used to produce poly(vinyl alcohol) (PVA) nanocomposites. The modified nanofiller was charac-terized with infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, scanning electronmicroscopy, transmission electron microscopy, and N2adsorption. When compared with pure meso-porous silica (MCM), the MCM@PEI nanoparticles exhibited better dispersion in the PVA matrix. Theeffects of MCM@PEI on the thermal and flame properties of PVA nanocomposites were also studied.Improvement in the thermal properties was confirmed by enhanced thermal stability and char yield.Incorporation of MCM@PEI in PVA led to a significant drop in the heat release rate and the total heatrelease.