Monodispersed polyisoprene-SiO2 nanoparticles were successfully synthesized by a differential micro-emulsion polymerization of isoprene on silane treated nanosilica. Core-shell morphology was formed consisting of silica as the nano-core encapsulated by polyisoprene (PIP) as the nano-shell, as confirmed by TEM. PIP-SiO2 nanoparticles were produced at 20-60 nm with a narrow size distribution resulting in a reduced nano-SiO2 aggregation in the PIP matrix. The influence of surfactant concentration, monomer/water ratio and SiO2 loading on particle size, monomer conversion as well as grafting efficiency was investigated. The monomer conversion was 87% and the polymer grafting efficiency was as high as 78% at an extremely low surfactant concentration (3 wt.% based on monomer). For rubber applications, the PIP-SiO2 nanocomposite has been used as an effective nano-filler in natural rubber (NR) latex and the NR filled with PIP-SiO2 prevulcanizate clearly showed an improvement in the storage modulus, tensile strength, tensile modulus, and anti-ageing properties. (C) 2012 Elsevier B.V. All rights reserved.