PURPOSE: To obtain a dermal collagen useful as a medical sewing thread, gauze, cosmetic, food packaging material, etc., by slicing a mollusk dermis with a little subcutaneous muscular tissue stuck thereto, drying the sliced dermis, and peeling the dermis.

CONSTITUTION: Epidermis of a mollusk, e.g. cuttlefish or octopus, is peeled, and the above-mentioned dermis with subcutaneous muscular tissue of 1W3mm, preferably 1.2W2.8mm thickness stuck to the dermis is sliced, dried, preferably at a low temperature or vacuum drying, and then the dermis is peeled from the above-mentioned muscular tissue to isolate the dermal collagen therefrom.