This study was conducted at the XINGLONGSHAN Musk Deer Farm of China from July to September 2008. Results showed that captive male musk deer exhibit aggressive dominance behavior, by which a stable social ranking is established. Generally, there were three types of aggression in agonistic interactions among males: attacking, displacing and threatening. Threatening was more frequently observed than displacing and attacking. When in conflict with other deer, high-rank males exhibited significantly more attacking than displacing and threatening. Moreover, no attacking occurred in low-rank and middle-rank males, but these individuals initiated significantly more threatening displays than high-rank individuals. Among musk deer groups with different social ranks, there were no significant differences between threats received by middle-rank and low-rank groups, but attacks directed to high-rank males was significantly lower than displacing and threatening behaviors. On the basis of these results, it is suggested that when a captive male musk deer population is assembled, individuals should be diversified in fighting ability and level of aggression. In particular, deer with higher aggression should not be enclosed with deer with similar tendencies, but should be enclosed with individuals with lower fighting levels. This should maintain stable social structures within captive musk deer groups and improve the overall welfare of captive musk deer.