Declared a global pandemic in March 2020, COVID-19 is unequivocally changing individuals' daily lives. Research suggests that for many people, the current pandemic is stressogenic, propelling myriads of disturbing affective experiences resulting in greater symptoms of depression and anxiety. Little is known, however, about how this ecologically grounded stress is experienced and managed within people's romantic relationships. Guided by the systemic transactional model of dyadic coping, the current study tested 4 preregistered hypotheses examining the effects of dyadic coping processes on partners' daily mood and relational outcomes near to the outbreak of COVID-19 (During May 2020). Using daily diary data collected from 72 Israeli couples over 21 days, the results showed COVID-related stress to be associated with lower daily positive, and higher daily negative, mood. Stress communication (i.e., disclosing stress to one's partner) was not associated with mood or relational outcomes; however, perceived positive and negative forms of dyadic coping (perceived partner's constructive and destructive behaviors in response to one's stress) were associated with poorer daily relational outcomes. Negative dyadic coping also exacerbated the effect of stress on one's negative mood. To the best of our knowledge, this is the first study to examine the effects of daily dyadic coping and COVID-related stress on people's affective and relational outcomes. The findings may shed light on the ways in which partners can help each other to adaptively cope with global health crises. (PsycInfo Database Record (c) 2022 APA, all rights reserved).