Abstract: Glass fiber reinforced PA66 (PA66/GF35) composites were reprocessed by the twin screw extruder.The effects of extrusion cycles on the rheological properties,thermal performance,glass fiber length and mechanical properties were investigated.The results showed that the melt volume flow rate of PA66/GF35 composites increased gradually and their apparent viscosity decreased significantly upon increasing the number of reprocessing cycle.For PA66 matrix,thermal oxidative degradation occurred during extrusion cycles,which led to the decrease of the intrinsic viscosity,the melting point,crystallization temperature and the degree of crystallinity,as well as the fraction of glass fiber and reduction of glass fiber length.Mechanical properties of PA66/GF35 composites were weakened with the increase of extrusion cycle.After four cycles extrusion,their tensile strength,flexural modulus and impact strength reduced by 38.41%,21.73% and 67.33%,respectively.