Among laboratory animals, pigs are anatomically and physiologically closer to human.Transgenic (TG) pigs can be widely applied as models of human diseases.Many researchers created TG pigs which have specific modified genome under a constitutively active promoter.A constitutively active promoter is effective to express a target gene, but the uncontrollable expression often results in unwanted outcomes.In this study, as a way to solve these problems, we tried to regulate the expression of target genes by tetracycline (Tet) on/off system.