Among of precursors polyacrylonitrile is one of the most promising materias for the manufacture of carbon fibers because filament form of polyacrylonitrile can be produced with high degree of orientation and heated to decomposition temperature without melting to give greater yield of carbon fiber. Carbon fiber manufacturing process are devided three major steps; stabilization, carbonization and graphitization but the first stabilization step is the most important process for carbon fiber quality control. In order to investigate the stabilization of PAN (polyacrylonitrile) precursor and copolymer, we prepared polyacrylonitirile homopolymer and IA (itaconic acid) copolymer by continuous polymerization process and studied thermal behaviour of these related precursors. The thermogravimetric behaviour of these copolymer is better than that of homopolymer because the rate of decreasing weight is much smaller than homopolymer. The IA copolymer has an initiating effect on the exothermic reaction and it also has a better weight retention in air atmosphere.