Humanitarian workers are frequently exposed to the traumatic experiences of others, placing them at risk for significant psychological consequences. While previous studies have examined some psychological impacts of this secondary exposure to trauma (SET), such as secondary traumatic stress (STS) and vicarious trauma (VT) separately, limited research has investigated the mechanisms linking SET to VT and the workplace and personal resources that may buffer these effects. The purpose of this study was to test the mediating role of STS in the relatiobship between SET and VT among humanitarian workers, and to examine whether perceived organizational support (POS) and psychological capital (PsyCap) moderated these pathways. Data were collected through an online survey using validated instruments from 51 humanitarian workers. PROCESS Model 75 in SPSS was applied to test a moderated mediation model. Results showed that SET significantly predicted STS. POS and PsyCap did not moderate the relatiobship between SET and STS, but both significantly moderated the path between STS and VT. Higher levels of POS and PsyCap weakened the positive association between STS and VT, confirming their buffering roles. Conditional indirect effects further revealed that STS mediated the link between SET and VT only when POS and PsyCap were low or moderate. These findings support the conservation of resources theory by highlighting STS as a mediator between trauma exposure and vicarious trauma, and underscore the importance of strengthening organizational and psychological resources to mitigate trauma-related outcomes among humanitarian workers.