Interpenetrating polymer networks (IPNs) were prepared by the sequential mode of synthesis using natural rubber and poly(methyl methacrylate) as the elastomer and plastomer components respectively. Two types of IPNs, viz. full and semi, were prepared and characterized by measurements of tensile strength, elongation at break, tensile modulus, tear strength and toughness and by scanning electron microscopy. Dicumyl peroxide and divinyl benzene were used as the crosslinker of natural rubber and comonomer/crosslinker for methyl methacrylate monomer, with benzoyl peroxide as the polymerization initiator. Effects of changes of blend ratio and extent of crosslinking of both plastomer and elastomer on the properties were examined. Full IPNs were characterized by higher tensile strength, modulus, tear strength and finer phase distribution than the corresponding semi-IPNs, but the latter exhibited higher elongation at break and toughness than full IPNs. © 1992.