This paper examines the conception of medical professionalism reflected in the Korean Medical Act. Several articles of the Korean Medical Act dictate that physicians should adhere to improved medical techniques or higher ethical standards in their field. The authority of professionals is grounded in their knowledge and expertise; indeed it is the nature of their authority that makes their professionalism necessary. The values of professionalism (expertise, morality, self-regulation, patient welfare) have traditionally been different from the values of commerce. In this article I argue that medical professionalism will be challenged if physicians must prove their innocence in medical malpractice litigation, as a current legislative bill stipulates. This article also reviews the problems associated with the burden of proof in such cases.