Polymers containing POSS(polyhedral oligomeric silsesquioxane) nanostructures show improved properties such as thermal stability, mechanical properties and oxidation resistance. Polyacrylonitrile(PAN) is one of the most widely used precursors for carbon fibers. However, PAN homopolymer has poor chemical, mechanical and thermal properties. A certain amount of suitable acidic comonomers is incorporated into PAN during polymerization for enhancing the solubility, the spinnability and especially, the thermo-oxidative stabilization. Among the acidic comonomers, IA(itaconic acid) is the preferably and the most widely used one because of the presence of two carboxyl group, which provides more opportunities for the carboxyl groups to interact with the nitrile groups during stabilization. In this work, we used Octa amic acid POSS having two carboxyl groups, to improve the properties of PAN copolymer. We investigated the effect of POSS addition during polymerization on the thermal properties of PAN copolymer. P(AN-IA)/POSS was prepared in dimethylsulfoxide (DMSO) by solution polymerization. Thin films of P(AN-IA)/POSS were prepared by spin coater using solution cast technique. The films were stabilized at different temperatures for various holding time. The structural evolution and the thermal properties of P(AN-IA)/POSS were studied by Fourier transform infrared spectroscopy (FT-IR), wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). From those results, the cyclization of nitrile groups was found to be initiated at lower temperature with increasing POSS contents and stabilization proceeded at more moderate pace in P(AN-IA)/POSS than PAN.