The molecular taxonomy of representative strains of gliding bacteria classified into two groups as Flexibacter maritimus (Group I) and Flexibacter sp. (Group II) in a previous report was determined. The average percent guanine plus cytosine (% G + C) of the deoxyribonucleic acid (DNA) of Group I was 32.24 which was within the range reported for F. maritimus. Though Group II had lower% G + C of 29.38, it was not significantly different from that of Group I. Polynucleotide sequence analysis determined by optical measurement of renatured DNA showed high homology values from 92 to 100 % among strains of Group I and Group II. In addition, the average similarity value derived from numerical taxonomy study was 82.7%. Based on these results, the two groups of gliding bacteria isolated from diseased cultured flounder are considered to belong to the same species of F. maritimus.