Outer space has become a vital part of international security. Since Sputnik, space has been gradually militarized, if not yet weaponized. During the Cold War, fierce competition between the two superpowers extended to space. In the post-Cold War period, new powers have joined the military competition in outer space, most notably China, India, and the European Union. Other middle-sized nations have also shown strong interest and made significant efforts in this area. Yet compared to the abundant literature on the space policy of major powers, there has been little study of the space policy of middle-sized states. To fill the gap, this article focuses on the evolution of South Korea's space policy as it relates to its national security: how Seoul's space policy will enhance, and has been enhancing, South Korea's military capability. After briefly outlining the development of security-related space policy in general, including South Korea's neighbors, Seoul's space policy is examined, including its current policies on space capability development, and the paper concluded by providing policy recommendations for Seoul's space policy.