Hydrogen Induced Cracking (HIC) is a major issue of line pipe steels exposed to sour environments. In general 5.0 wt% NaCl and 0.5 wt% CH3COOH solution with 0.1 MPa H2S provided by NACE TM0284 as solution A is used to evaluate the HIC resistance of steel plates and pipe products. However in many cases the test condition is too severe compared to the actual field conditions. Therefore Fit-For-Purpose (FFP) HIC evaluation method has been the subject of considerable investigations in recent years. High Strength Line Pipe (HLP) Committee of The Iron and Steel Institute of Japan (ISIJ) is investigating an appropriate test solution for FFP HIC test from the viewpoint of pH stability because pH is a significant factor affecting HIC behavior along with H2S concentration. In our previous work we proposed the test solution that provides high buffering capacity due to high concentration of acetic acid and sodium acetate. In this study HIC test were carried out in the several buffer solutions and the effect of pH shift on HIC behavior was investigated. The pH stability of high acetic acid and sodium acetate solution under low H2S partial pressure is also discussed because FFP HIC test tends to require long test duration in mildly sour environments (low H2S and high pH).