A total of 140 museum specimens of 7 different species of sea snakes, Emydocephalus ijimae, Hydrophis cyanocintus, H. melanocephalus, Laticauda colubrina, L. laticau-data L. semifasciata, and Pelamis platurus, were examined. Snout-vent length (SVL), head length, head width, head depth, and tail length were measured. Females had larger SVLs than males in H. cyanocinctus and P. platurus. All head variables of females were larger than those of males in L. semifasciata. Female head lengths were larger than those of males in P. platurus, whereas males' head widths and depths were larger than those of females in H. melanocephalus. Tail lengths of male H. cyanocinctus, H. melanocephalus, and L. semifasciata were greater than those of the respective females.