Core-shell natural rubber (CSNR), or encapsulated NR, was obtained by admicellar polymerization of poly(methyl methacrylate)-co-poly(3-trimethoxy silylpropyl methacrylate) (PMMA-co-PMPS) covering onto the NR particles. The core-shell structure was clearly observed in TEM micrographs. The presence of siloxane crosslinks in the shell was confirmed by FT-IR spectra. The obtained CSNR (containing NR core 70.85wt% and polymeric shell 29.15wt%) at 1-10wt% loading was used to improve toughness and mechanical properties of PMMA. SEM micrographs revealed that the CSNR had excellent compatibility and good interfacial adhesion to the PMMA matrix. The impact strength of CSNR-PMMA blends increased with CSNR content having the maximum at about 5.85kJ/m(2), which is 23% higher than neat PMMA (4.58kJ/m(2)). The elongation at break clearly improved to the maximum at 5wt% CSNR, and tensile toughness was about 219% higher than for neat PMMA, while elongation was about 91% higher than for neat PMMA. Several toughening mechanisms (rubber cavitation, plastic yielding of the matrix, and partial pull-out of rubber) appeared in the impact test, while the mechanisms for tensile toughening included rubber cavitation and crazing.