Present paper concerns with the accuracy and usefulness of pH determination in terms of freshness of fishes. A special glass electrode (Fig. 1) connected with an amplifier capable of reading exactly 0.50mV intervals was used. The results obtained are shown in Fig. 2-5 and Tab. 1-4, and may be summarized as follows: (1) The pH value of fish meats will be adopted as a criterion of the freshness of fishes to some extent. (2) However, the pH value varies according to the part of a body. And some divergencies are also observed according to the fishing season and species of fishes. (3) The pH value of fish meats at the early spoilage was 6.85 in the fishes of white meat and 6.27 in those of red meat.