BACKGROUND Caregivers of persons with dementia (PWD) can experience loss and grief long before the death of the PWD, with such caregiver grief postulated to affect the well‐being of the PWD‐caregiver dyads. However, the longitudinal effects of caregiver grief and the moderating effects of social services are not yet clear. OBJECTIVES We investigated the longitudinal effects of caregiver grief on caregiver depression, caregivers' quality of life (QoL), and caregivers' perceived positive aspects of caregiving (PAC); and examined potential effect modification of social service utilization (dementia care services, caregiver programs, and paid caregivers). DESIGN AND SETTING A prospective cohort study with three time points of assessments (at 0, 6, and 12 months). PARTICIPANTS Family caregivers of community‐dwelling PWD (n = 178). MEASUREMENTS At time point 1 (baseline), participants completed questionnaires that captured caregiver grief, burden, and social service utilization. Outcomes that were captured over time were: depression (time points 1–3), QoL (time point 2), and PAC (time point 3). Caregiver grief as well as interaction terms with social service utilization were included in Tobit regression to examine the association with outcomes. RESULTS: After accounting for the effect of caregiver burden, caregiver grief remained associated with depressive symptoms (P <.001) and poorer QoL (P <.001). However, compared with burden, grief contributed to larger magnitudes of the adverse effects. Grief, not burden, was associated with less PAC (P =.006 and P =.746, respectively). In contrast, burden, not grief, was associated with poorer physical health (P =.010 and P =.110, respectively). Dementia care services attenuated the effect of burden but not grief; caregiver programs did not affect burden but appeared to aggravate the effect of grief; and paid caregivers attenuated the effect of burden, and partially attenuated the effect of grief. CONCLUSION: Caregiver grief has an impact on dementia caregivers, likely through a distinct mechanism from that of caregiver burden. However, prevailing social services may not be sufficient to address grief, highlighting the need to further train care workers in this respect. J Am Geriatr Soc 68:2348–2353, 2020.