Cyber cooperation between Indonesia and Australia in the Defense Cooperation Arrangement is one of the Ministry of Defense's efforts to increase its cyber capacity. Defense cooperation between the two countries has existed for a long time, even before DCA existed. However, regarding cyber cooperation, this is certainly a new scope of cooperation. The research problems are about the challenge for Ministry of Defense to be able to increase its cyber defense capacity building through this cooperation. The purpose of this research is to analyze the current cooperation and determine possible actions to improve cyber defense capacity building. This research employs qualitative method. The research data were obtained from informants that had been previously determined, which were then analyzed using qualitative analysis technique. The results demonstrate that cyber cooperation with Australia is realized through various actions aimed at enhancing human competence in cyber. This includes awareness raising, cyber education, and cyber professionals training. But the implementation is still very low. Efforts to increase cyber defense capacity building must be carried out by optimizing existing cooperation. In addition, there is a need for coordination and communication forums between government agencies related to cyber cooperation. As the conclusion, cyber cooperation between Indonesia and Australia in the defense sector is still in the stage of establishing cyber defense capacity building.