The effects of glass fiber content and injection pressure on the mechanical and dynamic mechanical properties of glass fiber reinforced nylon 6 plastics were studied. On increasing glass fiber content, the fiber orientation, initial modulus, storage modulus and glass transition temperature increased, but the total energy dissipation in the glass transition region decreased. It was also found that the fiber orientation and the modulus had a maximum value at some critical injection pressure as the injection pressure increased. The reversed tendency was found in total energy dissipation.