Using some microscopic investigation, such as, plastic work absorbed in the intense strain region aroudn the blunted crack tip, crack opening displacement and fracture surface micro-roughness, the strain rate effect on fracture toughness and fracture resistnace characteristics of A533b-1 nuclear pressure vessel steels wree examined in quasi-dynamci test condition. J-integral based on the deformation theroy show strong dependence on size and geometry of specimen. But modified-J could be regarded that it is independent of the size and geometry, so it is possible to construct J-R curves with more valid data point for small specimen. Jw, calculated from recrystalization etching techniques gave same values as modified-J when the amount of crack extension is less than 1.5mm, and critical COD and tearing modulus basecd on COD showed good relationship with Jm and Tjm in that range. Local fracture strains were calculated from fracture surface micro-roughness, and were in the range of 1.8 and 2.0 which were much higher than the macroscopically measured one. It was nearly independent of strain rate and coudl be regarded as a material constant in fully ductile dimpled rupture. As a result, fracture toughness increased with strain rate increase but tearing modulus showed little variance. Such a high fracture thoughness values was mainly due to the high flow stress at high strain rate.