Acid-soluble collagen (ASC) and pepsin-soluble collagen (PSC) from flatfish skin were characterized. The yield of PSC was 85.5%, which was higher than that of ASC at 57.3%. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) patterns showed that both the ASC and PSC were consisted of ${alpha}1$ and ${alpha}2$ chains, and ${eta}$- chain. According to the results of Fourier transform infrared (FTIR) spectroscopy and hydroxylation, no difference in the helical structure between ASC and PSC was found. Thermal denaturation temperature (TDT) of flatfish skin collagen was $26.6^{circ}C$ for ASC and $26.7^{circ}C$ for PSC, which were similar to those of temperate fishes, while were lower compared to tropical fishes, such as the conger eel and Nile perch. There was no solubility difference between ASC and PSC at various pH and NaCl concentrations. Therefore, PSC will be preferable compared to ASC for commercial uses because of its higher yield.