The aim of this study was to investigate daily positive humor in couples as an interpersonal emotion regulation strategy. Associated changes in psychological intimacy were tested as a possible socio-affective pathway of emotion regulation that mediates the effects of couple humor on changes in individual momentary affect. Within a dyadic ambulatory assessment framework, 102 couples reported on their production of positive humor as an attempt to regulate their partner’s mood, psychological intimacy, and momentary affect four times a day for 1 week. An actor–partner interdependence mediation model revealed actor and partner effects of humor on changes in daily affect. Furthermore, the indirect effect of own humor via changes in the partner’s feelings of psychological intimacy (socio-affective pathway) on the partner’s affect was significant. Results support the assumption that daily positive humor experienced with one’s romantic partner serves as an interpersonal emotion regulation strategy in daily life as reflected in direct effects on one’s own and one’s partner’s momentary affect. The partner’s changes in affect were partially mediated by changes in their feelings of psychological intimacy. This speaks in favor of an indirect socio-affective mechanism of interpersonal emotion regulation associated with positive humor expressed toward the partner.