A method for separation the collagen from the various animal tissues is disclosed for preparing collagen solution and product using the same. The porcine tissues are processed to have proper form and size for acid-treatment. The acid-treatment is repeated with pepsin to separate type I or II collagens. The separated collagen is salt-treated for fractionation and ethanol-treated for obtaining 5˜10% of collagen from the initial tissue weight. The prepared tissues are processed for separating collagen through the collagen separating process. The separated collagen is processed for preparing product. The method for preparing product is comprised: treating a collagen solution having a predetermined concentration under a neutral condition at a low temperature, followed by overnight treatment at a temperature of 30 to 35° C.; concentrating collagen by centrifugation; and dissolving the thus-concentrated collagen in refrigerated weakly-acidic solvent or phosphate buffered saline (PBS), thereby preparing collagen having a concentration of 1 to 5 mg/mL.