The genetic relationships and taxonomic status of 7 taxa belonging to the genus Tridentiger (Pisces, Gobiidae) were investigated by means of analysis of allozymic variation at 14 loci. The results suggest that the two taxa “T. obscurus” and “T. brevispinis” which are sympatric and morphologically similar are reproductively isolated and are highly divergent from each other (the genetic distance values are 0.501-0,707). It is also suggested that “T. brevispinis” and “T. kuroiwae” are genetically different enough from each other to deserve subspecies at least. The other 4 taxa, “T. barbatus”, “T. nudicervicus”, “T. trigonocephalus” and “T. bifasciatus”, are genetically divergent each and are considered to be 4 biological species. A dendrogram showing the phylogenetic relationships of the 7 taxa was constructed from the genetic distances.