question: BACKGROUND: The coronavirus disease 2019 (COVID-19) pandemic led to measures that reduced social contact and support. We explored whether UK residents with more frequent or supportive social contact had fewer depressive symptoms during March-August 2020, and potential factors moderating the relationship. METHODS: A convenience sample of UK dwelling participants aged â©¾18 in the internet-based longitudinal COVID-19 Social Study completed up to 22 weekly questionnaires about face-to-face and phone/video social contact frequency, perceived social support, and depressive symptoms using the PHQ-9. Mixed linear models examined associations between social contact and support, and depressive symptoms. We examined for interaction by empathic concern, perspective taking and pre-COVID social contact frequency. RESULTS: In 71 117 people with mean age 49 years (standard deviation 15), those with high perceived social support scored 1.836 (1.801-1.871) points lower on PHQ-9 than those with low support. Daily face-to-face or phone/video contact was associated with lower depressive symptoms (0.258 (95% confidence interval 0.225-0.290) and 0.117 (0.080-0.154), respectively) compared to no contact. The negative association between social relationships and depressive symptoms was stronger for those with high empathic concern, perspective taking and usual sociability. CONCLUSIONS: We found during lockdown that those with higher quality or more face-to-face or phone/video contact had fewer depressive symptoms. Contact quality was more strongly associated than quantity. People who were usually more sociable or had higher empathy had more depressive symptoms during enforced reduced contact. The results have implications for COVID-19 and potential future pandemic management, and for understanding the relationship between social factors and mental health.