Synthesized of Polyaniline by polymerization of aniline using chemical oxidation with APS as oxidant. Subsequently, the nanocomposite was synthesized at different weight ratio of PbS and MnO2. The characterization of prepared nanocomposite by XRD, TEM and FT-IR. The sharp peaks of XRD indicate the high degree of crystallinity of the nanocomposite. The characteristic FT-IR peaks for PANI-PbS Nanocomposite indicated the PbS and MnO2 dispersed in the polymer matrix. The Thermal stability of Nanocomposite compared with pure PANI using TGA and DTA. It is observed that thermal stability of PANI/PbS and PANI/MnO2 are maximum as compared to bulk PANI.