Studies are divided on the effect of day-night temporal differences on clinical outcomes in out-of-hospital cardiac arrest (OHCA). This study aimed to elucidate any differences in OHCA survival between day and night occurrence, and the factors associated with differences in survival.This was a prospective, observational study of OHCA cases across multinational Pan-Asian sites. Cases were divided according to time call received by dispatch centers into day (0700H-1900H) and night (1900H-0659H). Primary outcome was 30-day survival. Secondary outcomes were prehospital and hospital modifiable resuscitative characteristics.About 22,501 out of 55,881 cases occurred at night. Night cases were less likely to be witnessed (40.2% vs. 43.1%, P < .001), more likely to occur at home (32.5% vs. 29%, P < .001), had non-shockable initial rhythms (90.8% vs. 89.4%, P < .001), lower bystander CPR rates (36.2 vs. 37.6%, P = .001), lower bystander AED application rate (0.3% vs. 0.7%, P < .001), lower rates of prehospital defibrillation (13% vs. 14.4%, P < .001), and were less likely to receive prehospital adrenaline (9.8% vs. 11%, P < .001). 30-day survival at night was lower with an adjusted odds ratio of 0.79 (95% CI 0.73-0.86, P < .001). On multivariate logistic regression, occurrence at night was associated with decreased provision of bystander CPR, bystander AED application, and prehospital adrenaline.30-day survival was worse in OHCA occurring at night. There were circadian patterns in incidence. Bystander CPR and bystander AED application were significantly lower at night in multivariate analysis. This would at least partially explain the decreased survival at night.