Crack tip solution chemistry is one of the key parameters controlling environmentally assisted cracking of structural materials in aggressive environments. Crack tip solution chemistry can be affected by the mass transport processes. Since laboratory tests are accelerated ones and are conducted only in a shorter period, crack growth behavior of material in operating plant condition may be different from the results obtained by laboratory tests. In this study, in order to investigate effect of exposure time on crack tip solution chemistry and crack growth rate of low sulfur low alloy steel in oxygenated high temperature water environment, a specimen was exposed in the environment for 1200 hours before corrosion fatigue crack growth test. The crack tip solution chemistry was evaluated by measuring crack tip electrochemistry potential and microsampling technique. The potential difference between crack tip and outer surface of the specimen was about 500mV. Anions such as chloride, sulfate and nitrate were found to be concentrated at crack tip during pre-exposure time of 1200 hours before test. During the EAC test under triangle loading mode, no crack growth was observed at an initial period of test which might be attributed to crack tip chemical blunting. However, after some amount of incubation time, suddenly, very high crack growth rate was observed which is as fast as those obtained in high sulfur steels.