Study objective: To investigate the association between family cancer caregivers’ unmet daily needs and emotional states of depression, anxiety and stress across their care recipient’s treatment phases. Method: A cross-sectional study design and self-report questionnaires were used. Family caregivers (N = 237) of cancer patients in ambulatory cancer clinics were recruited from May to December 2017, and completed a sociodemographic and medical questionnaire, the Depression Anxiety Stress Scale and Needs Assessment of Family Caregivers-Cancer Scale. Hierarchical linear regression was conducted to examine the influence of each predictor (sociodemographic variables, unmet personal care and role management needs, cancer treatment phase) on the Depression Anxiety Stress Scale total score, depression subscale, anxiety subscale, and the stress subscale. Results: Family caregivers’ unmet daily activity needs, in particular higher unmet personal care needs, during the intermediate phase (6–9 months), were significantly associated (ps<0.05) with overall distress (b = 4.93) and stress (b = 2.26). In the chronic treatment phase (>9 months), the significant association of unmet personal care needs was with overall distress (b = 5.91), anxiety (b = 1.97) and stress (b = 2.53). After completing treatment, unmet role management needs were only significantly associated with stress (b = -1.59). Caregivers’ higher depression was also associated with greater unmet role management needs, regardless of treatment phases. Conclusions: Intermediate and chronic cancer treatment phases were identified as having greatest effect on caregivers’ unmet daily activity needs and emotions. Unmet personal care needs played the major effect on overall negative emotional states in the intermediate treatment phase and stress in the chronic treatment phase. Close attention to caregivers needs in intermediate and chronic treatment phases, would be highly beneficial in alleviating negative emotional disturbances.