Abstract: The age and size composition, growth rate and reproductive biology of a cyprinid fish Gobio gymnostethus which is endemic species were studied in Aksaray-Melendiz Creek. The minimum and maximum fork length for female and male were 39.25-145 and 39.10-132.2 mm, respectively. Age distribution of Gobio gymnostethus populations living in Melendiz Creek ranged between 0 to VII. Sexual maturation age of Gobio gymnostethus for male and female was I year age and reproduction period of this species were April to July.