The effects of -ray radiation on PBO fibers and its composite materials have been investigated, the results showed that the microstructure and the performance of radiated PBO fibers have been improved with 30-120 kGy radiation dose, crosslinking reactions came from PBO polymer molecule chains and micro-fibrils. As a result, the molecular weight the thermal stability were increased, the tendency of micro-fibrils to split-off also decreased, the hook force of radiated PBO fibers increased by 14.0% without tensile strength loss, and the nano-compression modulus and the flexure strength of radiated PBO fiber composites also increased by 21.0% and 22.7%, respectively. The work indicated that -ray radiation could synchronously strengthen the microstructure and improve the properties of PBO fibers. POLYM. ENG. SCI., 58:272-279, 2018. (c) 2017 Society of Plastics Engineers