Abstract: Suicide is a significant public health concern among the military population. Thus, it is vital to understand suicide risk factors in this population. Alcohol use and post-traumatic stress disorder (PTSD) have been identified as risk factors for suicidality, whereas belongingness has been identified as a protective factor. This study aims to further clarify these relationships by examining the moderating effect of PTSD symptoms on the association between alcohol use and suicidality, and between belongingness and suicidality. We conducted secondary data analysis from currently serving members' surveys included in the Military Suicide Research Consortium Common Data Elements (MSRC-CDE) database (N = 2,361). Multiple linear regressions were conducted to examine the associations of alcohol use, belongingness, and PTSD symptoms on suicidality. Findings showed a significant interaction between alcohol use and PTSD symptoms, and between belongingness and PTSD symptoms, suggesting that PTSD symptoms moderated both associations. At lower PTSD symptoms levels, higher alcohol use was associated with higher suicidality. At higher PTSD symptoms levels, lower belongingness was associated with higher suicidality. These findings highlight the importance of screening and treating military personnel for PTSD, given that with its interaction with higher alcohol use and decreased belongingness, PTSD may increase the risk for suicidality.