Free radical polymerisation was employed for the preparation of homopolymer, poly (4-formyl-2-methoxyphenyl methacrylate) (FMPMA) and 2,2-azo-bisisobutyronitrile (AIBN) used as initiator in N,N-dimethylformamide (DMF) as solvent. Different concentrations of cadmium sulphide nanoparticles were embedded in a poly (FMPMA) matrix by in situ technique. Poly (FMPMA) and CdS/FMPMA nanocomposites were characterized by Fourier transform infrared spectroscopy (FT-IR) and structural characterization of CdS in nanocomposite was done by X-Ray diffraction (XRD). The XRD data showed CdS to have 2.49-3.56 nm diameter with cubic structure. Thermal characteristics of poly (FMPMA) and polymer nano composites were obtained from thermogravimetric analysis (TGA) and kinetic parameters of poly (FMPMA) and polymer nanocomposites were calculated using Broido method.