Feasibility of zone electrophoretic method using cellulose acetate film as a supporting medium was examined for species differentiation of some commercially important fish in kinship each other, since a need has arisen for proving a case of mislabling of fish, particularly in frozen forms. So far tested, cellulose acetate strips prepared by Courtlauds Limited of Conventry for Oxoid Ltd. gave a more satisfactory separation of soluble muscle protein than those of Separax. Procedure suggested in the present paper starts with one minute's blending of flesh portion of fish with equal volume of veronal buffer (pH 8.6, I=0.05), then centrifuge at 5, 000 rpm after 30 minutes, extraction in a refrigerator at 5°C and supernatant thus obtained is subjected to the electrophoresis under a current of 0.6mA/cm from 30 to 60 minutes. The zone development is made by staining each strip with 0.8% solution of Ponceau 3R for one minute with subsequent washing with 5% acetic acid for six minutes in order to remove unfixed dye on the strip. The species studied covered gurnard, yellowtail, mackerel, horse mackerel, plaice, cod, Alaska pollack, shrimps, and queen crab. Reproducible patterns from these examinations were considered to be employed to identify the species in question. Interesting finding to note was a close similarity in the patterns between two queen crabs, which have been regardedtaxonomically different species.