Determination of phenols with 4-aminoantipyrine is stated in the Standard Method of Analysis for Hygienic Chemists authorized by the Pharmaceutical Society of Japan and in various standard methods. This method is not evident from the viewpoint of the applicability for determination of various phenols, and the meaning and evaluation of results obtained by the method. Therefore, comparison of color development of phenol derivatives with 4-aminoantipyrine, reactivity of phenols with free residual chlorine, and the effect of reactants on the formation of antipyrine dye were examined. Results of recovery tests and intensity of color development using phenol derivatives indicated that this method can measure at ppm levels phenol derivatives such as o- and m-cresols, o, m-, and p-chlorophenols, dichlorophenols (except 2, 3-, 3, 4-, and 3, 5-dichlorophenols), p-bromophenol, o-, m-, and p-methoxyphenols, and o-allylphenol in city water and fresh water. The relationship between absorbance at 460 nm and phenol derivative concentration showed liniality below 80 μg of phenols. Concerning the effect of reactant phenol derivatives and free residual chlorine on the formation of antipyrine dye, phenol showed decrease of absorbance at 460 nm with increasing concentration of free residual chlorine and length of reaction time. Phenol derivatives have three patterns of changes ; rapidly decreasing, nonchangeable, and slightly increasing.