Population ecology of Cobitis tetralineata was examined at Churyeong Stream, Seomjin River, Korea. C. tetralineata inhabited on the sand bottoms with $10{sim}20cm/see$ in current velocity, and $30{sim}150cm$ in water depth. This species was active on the sand during the daylight hours from March to October, but they hibernated in the inside of the sand during the winter season. Sex ratio of female to male was 1:0.57, and female was $20{sim}30mm$ (TL) larger than male. The age group of C. tetralineata (female) population showed that the $20{sim}40mm$ group is 0+ years old, the $45{sim}65mm$ group 1+ years old, the $65{sim}90mm$ group 2+ years old, and the group longer than 90 mm over 3 years old. Males $13{sim}14$ months old after hatching had lamina circularis at the base of its pectoral fin as a secondary sexual character. And in its spawning season, lateral color pattern of male was changed as a sexual dimorphism. The spawning season may be from late June to middle July, $22{sim}26^{circ}C$ water temperature. The average number of mature eggs in ovary was about $1,288{pm}583(474{sim}2,976)$, egg diameter was about $0.98{pm}0.1mm$. C. tetralineata fed mainly on Chironomidae, Arcellidae, Branchioda and Algae. The feeding rate was the highest in April and September, but they did not fed in the winter.