Causal attributions of mental illness have received substantial attention given their influence on help-seeking patterns of individuals and the level of engagement with health services. Few studies, however, have examined caregivers’ perspectives of their relatives’ illness. The current study aimed to examine caregivers’ causal attributions of their relatives’ mental illness and its association with perceived stigma in a multi-ethnic Asian sample. Primary caregivers (N = 350) of psychiatric outpatients were recruited from a psychiatric hospital. The attribution and stigma sections of the Family Interview Schedule (FIS) were utilized to obtain caregivers’ causal report of their relatives’ illness and stigma perception. Logistic regressions were performed to examine the socio-demographic and diagnostic correlates of the four categories of causal attributions (psychosocial, biological, drug-/substance use-related, supernatural). The majority of caregivers identified psychosocial causes, followed by biological, supernatural, and lastly drug-/substance use-related causes for their relatives’ illness. Marital status, religion, employment status and the diagnosis of depressive disorders were significant correlates of biological attributions. Ethnicity and not knowing their relatives' diagnosis were significantly associated with psychosocial attributions. For drug-/substance use-related attributions, ethnicity was the only significant correlate. Supernatural attributions did not yield any significant associations. Caregivers who endorsed drug-/substance use-related reasons also reported significantly higher stigma than caregivers who did not endorse these attributions. A tendency to endorse biological and psychosocial causes for their relative’s illness was noted among caregivers. Further research on caregivers’ causal attributions is warranted to account for and replicate current study findings.