Nucleotide sequences of the small-subunit (SSU) ribosomal DNA were determined for Pelvetia babingtonii, P. canaliculata, Pelvetiopsis limitata, and Ascophyllum nodosum in the family Fucaceae. A total of 1755 positions were aligned for the whole sequence. The positional differences in the primary structure among the taxa ranged from 16 to 30 nucleotide changes in pairwise comparisons. There was a minimum between Ps. limitata and P. canaliculata. The SSU rDNA trees showed that the genus Pelvetia was not monophyletic and the genus Pelvetiopsis was not closely related to Pelvetia. Our results suggest that the taxonomic revision of the genus Pelvetia as well as the family Fucaceae is needed based on detailed morphological obsrvations.