Polypyrrole (PPy) was synthesized and doped with 1, 2, 4, and 8 wt.% of functionalized multi-wall carbon nanotubes (MWCNTs) by in situ polymerization. TGA/DTA analysis of nanocomposites revealed an increase in thermal stability by increasing the CNTs wt.%. Measurement of electrical resistivity showed a reduction in the resistivity of the composites at all temperatures. The glass transition temperature (T-g) of the samples was measured using electrical resistivity measurements and showed that by increasing the amount of functionalized MWCNTs in PPy, its T-g was increased. Temperature dependence of resistivity of pressed pure PPy showed that by increasing the pelletization pressure, the T-g increased. Also the hardness of nanocomposites was increased by increasing the MWCNTs wt.%.