Sozialstaat in constitutional law means the state that follows the guidance principle of “real freedom and equality.” According to the current Korean Constitution, this principle of Sozialstaat consists of social security and welfare, special protection of minorities, positive discrimination, guarantee of adequate economic and cultural life, protection of workers and their fundamental rights, optimal distribution of income, realization and guarantee of environmental rights, rights to an education, etc. In this situation, the author thinks it is necessary to consider the realistic possibility of the principle of Sozialstaat through the incorporation of international law into domestic legal system as the mixture of two different legal systems and the penetration of international law into domestic law have expanded. Recently, international law, in the form of customary international law as well as treaty, containing the principle of Sozialstaat such as human rights and environmental protection has rapidly and widely proliferated. Accordingly, the active incorporation of these international norms into domestic legal system will contribute to the realization of the principle of Sozialstaat. In this respect, incorporation of international law containing the principle of Sozialstaat into domestic law is a normative way to realize the principle of Sozialstaat. Therefore, the existing provision of Korean Constitution recognizing general incorporation of international law into domestic law and direct effect in domestic legal system is appropriate for the principle of Sozialstaat. However, the relevant constitutional provision and practice should be more developed and advanced so as to incorporate international law containing the principle of Sozialstaat into domestic law more actively. This stance will not only conform with but also contribute to the realization of the principle of Sozialstaat. In particular, according to the fact that principal contents of the peremptory norm of general international law, so-called jus cogens, are closely related to the principle of Sozialstaat, it is desirable to recognize that the jus cogens containing the value and contents of the principle of Sozialstaat is supreme law in our domestic legal system. The author thinks there should be interdisciplinary research and study as well as continuous attention and effort for development of desirable constitutional provision and practice on this matter. Based on this recognition, this paper reviewed and analyzed the desirable direction of operation and development of the Korean constitutional law and practice to realize and reinforce the principle of Sozialstaat, particularly focusing on not only theoretical and empirical study concerning the relation between international law and domestic law but also incorporation of international law containing the principle of Sozialstaat into domestic law. The author, through this discussion, hopes that more advanced and active constitutional practice including the amendment and improvement of constitutional provision will be achieved, which could help in realizing the principle of Sozialstaat in Korea.