The present invention relates to a porcine alpha-S1-casein gene, a porcine alpha-S1-casein gene promoter, an expression comprising the same promoter, and a method for the production of a target protein using the same expression vector. The promoter of the present invention facilitates the mammary gland-specific expression of the target protein. Accordingly, an animal transformed with the promoter secretes the target protein in milk at high concentration, and thus can be advantageously used for the production of useful proteins.