This paper deals a novel method for the synthesis of PbO nanoparticles by biochemical reaction between lead salt solution and leaf extract of Coriandrum sativum and facile, rapid & eco-friendly microwave assisted synthesis of two polymers poly methyl methacrylate & poly butyl methacrylate and two nanocomposites PbO/Poly methyl methacrylate (PbO/PMMA) and PbO/ Poly butyl methacrylate (PbO/PBMA). The synthesized nanoparticles were characterized by FT-IR, UV-visible, X-Ray Diffraction (XRD) and Transmission Electron Microscopic (TEM) studies. Nanocomposites were characterized by FT-IR, Scanning electron microscopy (SEM) and TG/DTA. XRD studies and TEM images revealed average particle size of synthesized nanoparticles 20 nm. Thermal studies revealed that overall thermal stability of PbO/PMMA and PbO/PBMA nanocomposites decreased due to incorporation of PbO nanoparticles in the polymer matrix.