Serum transferrin (Tf) is an iron (Fe)transporting protein with the property of reversibility in binding Fe. Cetaceans are aquatic mammals that exhibit particularly high Fe bioavailability in the body. However, little is known about serum Tf in cetaceans to date. The goal of this study was to determine the special characters of serum Tf between cetacean species and several other vertebrate groups. Zones and types of serum Tf of cetacean bottlenose dolphin(Tursiops truncatus) and roughtoothed dolphin(Steno bredanensis) were studied comparatively, for the first time, with bottomliving yellow catfish(Pelteobagrus fulvidraco), sha rptooth catfish(Clarias leather), turbot(Scophthalmus maximus), margined bullhead(Liobagrus marginatus), Chinese sturgeon(Acipenser sinensis), amphibian tiger frog(Rana tigrina), terrestrial mice(Mus musculus) and human (Homo sapiens). Electrophoretic separation of Tf was performed using discontinuous polyacrylamide gel electrophoresis (PAGE). An ironspecific stain method was used to identify the Tf and other Febinding proteins. Results suggested that the Tf zones were divided into four areas (Tf ITf IV). Serum Tf possessed 4-6 bands in the bottlenose dolphins and 5 Tf bands in the roughtoothed dolphin. These two Tf types in cetacean species were usually more complicated than those of human and other animals studied except for tiger frog. In addition, cetacean serum Tf distributed more widely across the serum Tf zones, and especially all serum Tf ITf IV zones in the bottlenose dolphin. The concentrative areas of serum Tf bands and their relative activities seemed to be different between cetaceans and other species, implying an adaptation for special water living habitats and respiratory patterns. Furthermore, although the serum Tf zone patterns among the three bottlenose dolphins were the same, the Tf bands were different from each other, suggesting the tendency of serum polymorphisms in serum Tf of the three bottlenose dolphins. Further research will be required to deepen our understanding not only of the cetacean serological characters on ironbinding, but also of the molecular weight, isoelectric point, amino acid component, and molecular basis of serum Tf in cetacean species. Key words:Tursiops truncatus; Steno bredanensis; serum transferrin; polymorphism; adaptation