The linear viscoelastic behaviors of nylon1212 blends toughened with (styrene-[ethylene-(ethylene-propylene)]-styrene block copolymer) (SEEPS) elastomer were carried out. The results show that dynamic storage modulus (G') curves of the blends are located between those of virgin nylon and SEEPS within the frequency (omega) tested, and the G' of blends increases with increasing of the SEEPS content. Moreover, the predictive results of Palierne emulsion model show that it is unsuitable for describing the viscoelastic behaviors of the double phase systems toughened with elastomer, especially for the system with high content of elastomer. The positive deviation in the plots of G' vs. blend composition demonstrates that the blends are immiscible. From the point of phase transition, the phase inversion region for these blends was predicted to be in the range of 30-50 wt% of SEEPS, which agrees with the morphology analysis of nylon1212/SEEPS blends. In addition, "Cole-Cole" plots of modulus at different temperatures show that the microstructures of blends are unstable in the phase transition region. (c) 2008 Wiley Periodicals, Inc.