In this study, lactic acid was used to extract chitin by decalcifying shrimp heads and shells of penaeus vanmamei with ultrasonic -assisted. A Box–Behnken design with three variables and three levels was applied in order to approach the prediction of optimal the lactic acid concentration, the liquid-solid ratio and the reaction time on the demineralization degree with lactic acid. These optimal conditional were: with the ultrasonic assisted, the lactic acid concentration of 11.50%, the liquid-solid ratio of 26:1(mL/g ),and the reaction time of 95 min allowing to obtain chitin, which ash content was predicted at 0.35±0.05(g/100g), and the chitin would be used in the food industry.