Objective: To explore the relationship between social support and quality of life (QoL) among family caregivers of persons with severe mental illness (SMI) and examine the mediating roles of care burden and loneliness. Methods: A cross-sectional study was carried out between December 2017 and May 2018. A random sample of 256 family caregivers of persons with SMI in rural areas of Sichuan Province, China was recruited for participation. Survey data on socio-demographics, social support, care burden, loneliness, and QoL were collected via in-person interviews. Multiple linear regression analysis and structural equation modeling (SEM) were used to test the hypothesized relationships. Results: The majority (72.7%) of family caregivers of persons with SMI in this study reported having low QoL. Social support was positively associated with QoL and negatively associated with care burden and loneliness. The findings suggested the mediating roles of care burden and loneliness on the association between social support and QoL. Conclusion: The hypothesized model was found to be a suitable model for predicting QoL among family caregivers of persons with SMI. The findings can help inform the design of future interventions aimed at enhancing social support, reducing care burden and loneliness, which may be helpful to improve caregivers' QoL. Future study is required to find a causal path to promote QoL among family caregivers of persons with SMI.