This paper investigates rheological and mechanical properties of poly(trimethylene terephthalate) (PTT) in presence of multi-walled carbon nanotubes (MWCNTs). Morphological characterization by scanning electron microscope and transmission electron microscope showed uniform distribution of MWCNTs in the PTT matrix. Incorporation of MWCNTs into PTT matrix resulted in higher complex viscosity (eta), storage (G') and loss modulus (GaEuro(3)) than those of neat PTT, especially in low-frequency region. The dramatic increase in melt viscosity of PTT observed upon incorporation of MWCNTs in the range of 0.25-1 wt% could be due to the formation of interconnected network of MWCNTs in the polymer matrix, and thus, this can be regarded as rheological percolation threshold concentration. Cole-Cole plot showed change in slope and also shift in G' versus GaEuro(3) plot, which suggested change in microstructure upon MWCNT addition. The reinforcing effect of MWCNTs was also confirmed by dynamic mechanical analysis, where, by adding CNTs, a noticeable increase in storage modulus of PTT was observed. However, addition of MWCNTs showed no significant effect on the tensile properties of PTT due to poor interfacial interaction between CNTs and polymer matrix.