Swimming pool water may accumulate chlorinated organic compounds because of continuous chlorination and contamination with organic compounds in the form of sweat, urine, epithelial cells, hair, etc. Some of these chlorinated compounds are suspected as carcinogens or mutagens. In this paper, we assayed the mutagenicity of 5 samples of swimming pool water in Kitakyushu-city. The samples were concentrated with adsorbent (CSP800) and the mutagenic activity was assayed on Salmonella typhimurium TA100 and TA98 strains with or without S9 mix. The water samples were also analyzed for volatile organic compounds and some factors prescribed by the conventional water quality surveillance protocol. The samples tested showed TA100 mutagenicity of 2,100 to 13,030 rev./L without S9 mix. High concentration of ammonia was detected in one of the samples, but not chloroform. The users of the facility, where the sample was obtained, had complained of eye irritation. In addition to ammonia, chloramine formed from ammonia and chlorine is known to be irritative to eyes and to give unpleasant odor in swimming pool water. Therefore, we examined the level of chloroform, residual chlorine, and the mutagenicity when ammonia was added to chlorine-treated humic acid as a model for generation of chlorinated organic compound. Chloroform level and the mutagenicity were decreased, while residual chlorine level was increased during chloramine formation.