Three component interpenetrating polymer networks (IPN’s) of polyurethane (PU)–poly(n-butyl methacrylate) (PBMA)–poly(methyl methacrylate) (PMMA) were prepared by the combined synthesis of simultaneous polymerization and sequential polymerization. Two types of IPN’s, (PU–PMMA)–PBMA and (PU–PBMA)–PMMA, were obtained by forming PU–PMMA (or PU–PBMA) simultaneous IPN’s first and then swelling the network in BMA (or MMA) and ethylene dimethacrylate (EDMA) monomer mixtures followed by sequential polymerization of the imbibed monomers. The glass transition behavior studied by DSC and DMA showed three separate but broad Tg’s for (PU–PMMA)–PBMA IPN’s, while two Tg’s (one broad Tg for PU. transition and the other broad Tg at intermediate temperature of PMMA and PBMA transition) were observed for (PU–PBMA)–PMMA IPN’s. Both three component IPN’s showed high damping characteristics (tanδ=0.2—0.4) in the temperature range of −30—90°C. The TGA analysis revealed enhanced thermal stability in all of the two-component and three-component IPN’s of polyurethane and polymethacrylate.