Purpose: To evaluate the quality of life (QoL) and social support among family caregivers of a family member with a mental illness and to identify factors associated with the QoL.; Methods: This is a cross-sectional study, where participants were recruited and independently interviewed using a questionnaire, consisting of demographic characteristics, the Medical Outcome Survey SF-36 form, and social support rating scales. Multiple stepwise regression analysis was used to analyse the factors related to QoL.; Results: 181 family caregivers were recruited in Shandong province, China. On a composite QoL score, family caregivers perceived that their QoL was poor (68.3), especially in the aspects of role-physical (61.3), role-emotional (57.6) and mental health (63.0). We also found family caregivers received low social support, especially in objective support and utilization of social support. Patient's illness state, care time, financial burden and objective support were significantly correlated to caregivers' QoL in the physical component score (PCS). Patient's illness state, patient's marital status, family monthly income, caregiver's knowledge about the illness, caregivers coordinating caring, life and work, subjective support received and utility of support were significantly associated with caregivers' QoL in the mental component score (MCS).; Conclusions: Social support had a significant correlation with caregivers' QoL. Caregivers should be encouraged to request assistance from other family members and friends in providing care, especially when caregivers are unemployed or long-time carers. Mental health education campaigns and helping families to maintain and enhance a supportive social network may provide useful means to improve caregivers' QoL.