Aside from economic and socio-cultural aspects Indonesia and South Korea maintain intense and mutually beneficial cooperation in security affairs. As middle powers both countries share aligned views on regional and global peace and security with ample capacity to play more influential roles. This article describes how Indonesia and South Korea uphold security cooperation by conducting defense diplomacy. Findings show that since bilateral relations were upgraded to a strategic partnership in 2006 until 2023 Indonesia and South Korea have made significant progress in aerospace and naval defense industry cooperation strategic communications and consultations and joint military exercises and security exchanges. However issues in financing technology transfer and geopolitical dynamics have caused obstructions in those fields. Furthermore several avenues of cooperation may be explored further and deeper in the future including maritime security cybersecurity counter-terrorism and multilateral engagement.Keywords Indonesia South Korea defense diplomacy security cooperation.