OBJECTIVES: To examine the influence of social disengagement and depressive symptoms on sleep disturbance among dementia caregiving dyads and the actor-partner interdependence nature of these influences. DESIGN: Actor-partner interdependence model through structural equation modeling for dyadic analyses. SETTING AND PARTICIPANTS: A total of 310 dyads of older adults with dementia and their care partners from 2 national representative studies in the United States, the National Health and Aging Trends Study (NHATS) and its companion study, the National Study of Caregiving (NSOC). METHODS: Data from the NHATS Round 11 and NSOC IV were analyzed using descriptive statistics, Pearson correlation analysis, and the actor-partner interdependence model. Structural equation modeling was used to assess the mediation effects of depressive symptoms within the actor-partner interdependence models. RESULTS: In the model of caregivers, social disengagement had a direct impact on sleep disturbance (β = 0.49, P < .001) and an indirect impact through depressive symptoms (β = 0.25, P < .001). In the model of older adults with dementia, social disengagement only had an indirect effect on sleep disturbance through depressive symptoms. In models examining partner effects, caregivers' social disengagement directly influenced their care partners' depressive symptoms (β = 0.20, P = .019), which subsequently affected caregivers' sleep disturbance (β = 0.17, P < .001). Social disengagement (β = 0.17, P = .001) and depressive symptoms (β = 0.17, P < .001) in older adults with dementia directly impacted their caregivers' sleep disturbance. Depressive symptoms of older adults with dementia served as multiple mediators linking one member's social disengagement to both their own and partner's sleep. CONCLUSIONS AND IMPLICATIONS: This study represents one of the first attempts to investigate the influencing mechanism of sleep disturbances among older adults with dementia and their informal caregivers through a dyadic perspective. The sleep disturbance of caregivers may be directly influenced by the social disengagement and depressive symptoms exhibited by both members of the dyad, whereas the sleep disturbance experienced by older adults with dementia can only be indirectly influenced by the dyad's social disengagement via their own depressive symptoms. Dyadic social activities targeting depressive symptoms could be designed to address sleep disturbances in dementia caregiving dyads.