Abstract: The solubility of pure phenylmercuric acetate in water was determined in intervals of 5° between the temperature of 0°-50℃. The solution was first saturated with the salt at a higher temperature, then cooled to the desired temperature and allowed to stand to reach equilibrium. Thereafter, a weighed portion of the solution was cautiously evaporated to dryness at 60°-70℃, the weight of the residue was determined and the solubility C was calculated. After smoothing out the observed values of C by the method of least squares, an empirical relation has been established between the most probable value, C, as expressed in g per 100 g solution, and the temperature, t(℃), as follows: C=0.246+0.00186t+0.0001948t² The observed value,C, and the calculated one, C, are fairly accordant in most cases. As a result, the most probable solubility found for 15°, 20° and 25℃ are 1:310, 1:280 and 1:240, respectively. Therefore the solubility of phenylmercuric acetate cited both in the British Pharmaceutical Codex 1949 and the Merck Index, as 1:600 at room temperature, is rather questionable.