Sequential interpenetrating polymer networks (IPNs) were synthesized using natural rubber (NR) and polystyrene (PS) as elastomer and plastomer components, respectively. Benzoyl peroxide was used as the polymerization initiator, dicumyl peroxide as the crosslinker for NR and divinyl benzene as the comonomer/crosslinker for PS. Both full IPNs and semi-IPNs were prepared and characterized by evaluating their mechanical properties. Morphology of the IPNs were studied through scanning electron microscopy. Effect of variation of blend ratio and degree of crosslinking (of both plastomer and elastomer) on these properties were studied. Full IPNs showed higher tensile strength, modulus, tear strength and finer phase distribution than the corresponding semi-IPNs while the latter exhibited higher elongation at break and toughness. © 1993.