Polypropylene (PP) nanocomposites filled with the pristine multi-wall carbon nanotubes (CNTs) and the purified CNTs were prepared by melt blending. The microstructure and linear viscoelastic properties wereinvestigated using rheological and morphological measurements. The results show that the purified CNTs disperse uniformly in the PP matrix. At low frequencies, frequency dependence of modulus weakens clearly with the addition of the CNTs, indicating that the long-range motion of the polymer chains is restrained by the presence of the CNTs. Percolation networks form when the loading levels achieve up to 3 and 1.5 wt% for the composites with the pristine CNTs (PPCNTs) and the purified CNTs (PPcCNTs), respectively. The linear relaxation modulus increases with increasing loading level. And for composites with loading levels above percolation concentration, the modulus appears to reach a plateau at long time scales due to the formation of percolation network. Tensile strength and impact strength are simultaneously improved with the addition of the CNTs. The better the dispersion of the CNTs, the greater the improvement of the tensile strength and the impact strength. POLYM. ENG. SCI., 2012. (C) 2012 Society of Plastics Engineers