Natural rubber grafted with poly(methyl methacrylate) (NR-g-PMMA) was prepared with a NR/MMA ratio of 90/10 by weight, and subsequently epoxidized in its latex state via in situ performic acid to create materials with epoxide contents of 10, 20 and 30 mol%. The grafting efficiency was 94.3% and the grafted PMMA content remained more or less unchanged after epoxidation. The changes of mate- rial polarity caused by the presence of epoxide groups at different levels in combination with the grafted PMMA clearly had effects on the thermal properties, wettability and swelling behaviors of the materials. The increase of polar functional groups and the presence of PMMA as ther- moplastic resulted in a higher glass transition temperature (Tg) and improved thermal stability. The shift in Tg and