The brook lamprey, Lampetra reissneri, was collected from an branch of the Nakdong River (Namwon-gun, Chollabuk-Do) and the Seomjin River (Hadong-Gun, Kyungsangnam-Do) from September, 1989 to April, 1990. Specimens were 95 individuals in number and composed of 21 ammocoetes, 16 metamorphosing animals and 58 adults which do not exceed 200mm in total length. The modal numbers of trunk myomer was 57.5, ranged from 55 to 60. In the dental formula, the supraoral tooth consistently had 2 cusps, and lateral circumorals were 3 in each side with 2 cusps. The infraoral had varying numbers of cusps ranging from 6 to 8. In morphological measurement of adults, prebranchial length was 10.3%, branchial length 9.7%, trunk length 51.3% and tail length 28.3% respectively, in hundreds of total length. No significant differences in morphological characteristics were observed between the two populations studied.