Removal characteristics and removal improvement in sewage treatment plant, and batch-type laboratory test were examined for organic chemicals such as bisphenol A (BPA), a suspected endocrine disruptor.The BPA removal efficiencies were 33-72% in a sewage treatment system, and the majority was carried out in the aeration tank. In the laboratory test, gross removal efficiency was 71%, of which about 40% was due to initial adsorption to sludge (IAS). Moreover, it was found that removal rate of BPA in the solution after IAS was almost equal to its degradation rate in the sludge.IAS was enhanced by increasing MLSS concentration and by reducing the BPA concentration, however, it was decreased as increasing frequency of usage in batch type activate sludge.IAS was restored by the modified reaeration process (MRP) applied to the sludge. It was thought that the appropriate time of reaeration was at least ten hours. MRP was also effective in the removal of other organic chemicals tested in this study. However, it was not effective for DIO (1,4-dioxane), a substance whose octanol/water partition coefficient (Log Pow) and biodegradation ratio were low.