The viscoelasticity of poly(trimethylene terephthalate)/thermoplastic polyester elastomer(PTT/TPEE) blends was investigated by dynamic mechanical analysis and rotational rheometer. The results suggest that the addition of TPEE can increase the toughness or damp properties in low temperature range. The cold-crystallization ability of PTT is also improved by TPEE which has more active molecular chains. The glass transition temperatures of blends decrease with TPEE content increasing, but the storage modulus increases. The complex viscosities of melts, shear storage modulus and elastic behaviors increase with increase of TPEE content, however, the viscous behaviors is prominent in the melt rheological behaviors. TPEE is a good modifying addition for PTT processing.