Among couples, sleep is theorized to be a dyadic process, within which relationship quality exerts a large influence (Troxel, Robles, Hall, & Buysse, 2007). In turn, research has shown that capitalization, or positive-event disclosure, influences relationship quality. The benefits of capitalization, however, are contingent on the receipt of a supportive response, here referred to as capitalization support (Reis & Gable, 2003). Accordingly, the current study examined daily capitalization support, loneliness, and intimacy as predictors of sleep (i.e., quality, duration, difficulty falling asleep). Post-9/11 military veterans and their spouses (N = 159) completed a 32-day internet-based survey assessing daily relationship experiences and health. Results of an actor-partner interdependence mediation model on aggregated daily data revealed actor indirect effects of capitalization support on sleep outcomes via loneliness and intimacy, for veterans and spouses. Partner indirect effects were observed for veteran capitalization support on spouse difficulty falling asleep and sleep quality, via spouse loneliness and intimacy. Lagged actor-partner models revealed similar actor effects for daily capitalization support on loneliness (spouses) and intimacy (spouses and veterans), which in turn uniquely predicted daily sleep. Partner effects were observed for veteran capitalization support on spouse intimacy, and veteran loneliness on spouse sleep quality. Results highlight potential new avenues for interventions to promote better sleep by promoting positive relationship functioning between romantic partners. Such work is especially important for high-risk individuals, including military veterans and their spouses for whom prolonged postdeployment sleep difficulties pose particular concern. (PsycINFO Database Record (c) 2018 APA, all rights reserved).