To improve the oxidative efficiency of polyacrylonitrile (PAN) precursors, modification of PAN precursors was employed by gamma ray irradiation. Effects of irradiation on the structure and properties of PAN precursors were investigated. The results showed that cyclized structure in the precursors was formed after -ray irradiation. Meanwhile, irradiation could reduce the heat evolved, relax the exothermic behavior, decrease the mechanical properties and enhance the density of PAN fibers. It is supposed that the modification of -ray irradiation could remarkably accelerate the stabilization process of PAN precursors and reduce the production cost of resulting carbon fibers. POLYM. ENG. SCI., 56:1313-1318, 2016. (c) 2016 Society of Plastics Engineers