It is well known that the TMCP steel rolled at the temperature of its intercritical region in steel production has high brittle crack arrestability. The cause is generally considered to be related with the generation of separations ahead the main brittle crack just in advance. However it has been sometimes experienced that there are no observation of appearance of separations on the brittle fracture surface for TMCP steel plate with high K _ca . Then in this study, we carried out not only double tensile tests but also COD tests and Charpy impact tests with various directions by using two TMCP steel plates, which are produced from same slab but are rolled at the different finishing temperature, thus leads to different maximum separation index. By analyzing these test results, it is understood that high K _ca value comes from zig-zag path of brittle crack which is caused by anisotropy of fracture toughness of steel plates.