This study examined domestic and international discussions on conscientious objection to military service and the implications of a major shift in judicial judgment led by the Constitutional Court and the Supreme Court, and suggested a reasonable model of an alternative civilian service system. The main content of this study is as follows. First, social discussions on conscientious objection began in 2004 when the Supreme Court’s decision was made on conscientious objection. For the next 15 years, in Korean society the social conditions have become favorable enough to recognize conscientious objection as the realization of freedom of conscience and to implement an alternative service system. Second, foreign cases show that alternative service systems generally require conscientious objectors to serve one to one and a half times the length of military service in the private sector. This is in line with the U.N. Human Rights Council’s recommendation that alternative services should not be punitive and should be of a public interest and (or non-combat) nature. Third, members of the National Assembly, the government and civil activists proposed various models of an alternative service system were proposed before and after the Constitutional Court ruled against Article 5 of the Military Service Act (type of military service). Among the various models, the civil society plan was uated as a model that could harmonize the fairness of military service with objectors’ freedom of conscience in terms of the contents, length, and methods of alternative civilian service. Fourth, we suggest the following alternative service system guidelines focusing on the main issues: alternative service is to be served in non-military social welfare and public areas for one to one and a half times the length of military service (exceptions may be allowed in consideration of the types of task ), and a review committee consisting of experts from various fields is to be established under the Prime Minister to enhance fairness and professionalism in the review of eligibility for alternative service.