Over the wide range of the loading rates, fracture toughness test have been carried out for the GFRP material. Fracture toughness based on the stress singularity is significantly affected by the loading rate, while one based on the strain singularity is less affected by the loading rate. Fracture toughness based on the strain can explain the fracture behaviors of viscoelastic materials, but to explain the loading rate effect completely, the debonding process between the glass fiber and the polymer matrix must be taken into account.