Glass fiber (GF) reinforced nylon 6 (PA6) composites were prepared with a twin-screw extruder. The effects of GF mass fraction on the mechanical properties, thermal properties, density, water absorption and processability of PA6/GF composites were systematically investigated. The results show that the impact strength, tensile strength, flexural strength, flexural modulus, density and thermal deformation temperature of the composites increased with the increase of glass fiber content, while the water absorption and melt flow rate decreased with the increase of glass fiber mass fraction. The morphology showed that the GF was effectively wrapped and dispersed in the PA6 matrix when the GF mass fraction was increased up to 30%.