Abstract: According to the center combination of experimental design, we extracted the gelatin from Oreochromis nilotica scale after decalcification by acid extraction with EDTA-Na₂ to study the effects of extracted time (h, X₁), extracted temperature (℃, X₂), acid treated time (h, X₃) and citric acid concentration (g·L^-1, X₄) on the yield (%, Y) of gelatin, and compared the physicochemical properties of the gelatin with bovine bone gelatin.The results of response surface methodology (RSM) indicate that the extracted temperature, extracted time and acid treated time affect significantly the yield of gelatin.The optimum conditions are 200 g·L^-1 citric acid concentration, 11.3 h treated time, 65 ℃ extraction temperature and 3.6 h extraction time.Under these conditions, the measured yield of gelatin is 28.4%, which is close to 30.1% of the predicted value.The content of crude protein, gel strength, melting point, logarithmic viscosity and the least concentration of the gelatin are 89.9%, 245 Bloom (g), 27.0 ℃, 0.030 L·g^-1 and 8.0 g·L^-1, respectively.The contents of glycine and imino acids (proline and hydroxyproline) are 352 and 173 per 1 000 total amino acids, respectively.