Multi-loci analysis coding to isozymes was made of 7 spawning populations of Pacific herring Clupea pallasi collected from 2 coastal waters (oceanic type) and 5 brackish waters (brackish type) in the northern Japan. Genetic polymorphisms were observed at 19 loci among 29 loci coding isozymes by starch gel electrophoresis. Greater degrees of polymorphic varia-tions were observed at the 4 loci in GPI, IDH, ME, and PGM. Average heterozygosities were significantly lower in the oceanic type than those of brackish type. Results of a contigency X2 analysis for homogeneity of allele frequencies over all loci of the samples suggested that these 7 populations are genetically isolated each other. However, the level of genetic distance (D) between them was rather low (D=0.0004-0.0035) and the level of differentiation between samples was estimated to be almost the same as those of local populations of other fish species so far reported. The 7 herring samples were clustered into 2 groups at the D value 0.0024. The first is the oceanic type including two local populations Ishikari and Mangoku-ura and the latter is the brackish type including five local populations Saroma, Notoro, Furen, Yudo and Obuchi.