The linear viscoelastic properties of one family of base asphalts, unmodified or modified by the simple addition of an elastomer or by further in-situ crosslinking, have been investigated. The time-temperature superposition principle was shown to be valid for the base as well as for the modified asphalts. The addition of the elastomer styrene-butadiene (SB) copolymer increased drastically the storage modulus and the elastic character of the asphalts. The thermal susceptibility of the polymer modified asphalts was considerably reduced and this combined with an increased resistance to deformation (larger complex modulus) suggests much better performances for road applications. The chemically modified asphalt containing 3% SB showed similar viscoelastic properties as the physical blend containing 6% SB.