Objectives: Existing studies indicate that the presence of social support increases the likelihood of caregivers experiencing feelings of gain from caregiving; however, researchers have not yet investigated the mechanism through which social support is linked to caregiver feelings of gain. Informed by Bandura's Social Cognitive Theory, the present study investigated whether a sense of caregiving mastery serves as a key mechanism. Method: Sixty-three family caregivers of dependent elders completed surveys to assess caregiver feelings of gain, socio-emotional support (from family, friends, spouse/partner) and mastery. To evaluate the hypothesized mediation model, a series of structural equation modeling (SEM) analyses were conducted with the maximum likelihood method by Lisrel 8.8. Results: Socio-emotional support from family members was found to be an important resource for caregiver feelings of gain. SEM analyses further revealed that the mechanisms by which socio-emotional support influences caregiver feelings of gain vary depending on its source (i.e. family members, friends, and partners). Conclusion: As hypothesized, caregiving mastery played a mediating role for non-partner family socio-emotional support whereas it did not for partner socio-emotional support. Based on availability or absence of specific sources of support, caregiver intervention programs should be individually tailored to enhance their potential impact.