Background/aim: Remdesivir, which was first developed for the treatment of Ebola disease but failed to meet expectations, has become hope in the fight against the COVID-19 pandemic. This study aimed to evaluate risk factors for mortality and prognosis of adult moderate/severe COVID-19 patients treated with remdesivir, and safety and tolerability of 5 days of remdesivir treatment. Materials and methods: This multicenter prospective observational study was conducted in 14 centers in Turkey. Pregnancy or breastfeeding, multiorgan failure, or usage of vasopressors for septic shock, ALT > 5 × the upper limit of the normal range, or eGRF <30 mL/min or dialysis and receiving favipiravir were the exclusion criteria of the study. Results: Among 500 patients, 494 patients were included in the study. On admission, 392 (79.3%) patients had moderate and 102 (20.6%) patients had severe COVID-19. The 28-day mortality was 10.1%. The median of the scores of the seven-category ordinal scale assessed on days 0, 3, 5, 7 were 4 and 3 on day 14. When the survival status of the patients was evaluated according to the time between the remdesivir start date and the end date of the symptoms, no statistically significant difference was found between the medians of the groups (p = 0.404). In multivariable analysis, age (OR, 1.05; 95%CI, 1.02–1.08; p = 0.003), SpO2 level on admission (OR, 3.03; 95%CI, 1.35–6.81; p = 0.007), heart rate (OR, 2.48; 95%CI, 1.01–6.07; p = 0.047), follow-up site at the hospital (clinic/ICU) (OR, 26.4; 95%CI, 11.6–60.17; p < 0.001) were independently associated with increased mortality. Grade 3 adverse event (AE) was observed in 4 (0.8%) patients. None of the patients experienced grade 4 or 5 AEs. Conclusion: Remdesivir is a safe and well-tolerated drug and older age, low SpO2 level on admission, tachycardia, and ICU admission are independently associated with increased mortality among patients with moderate/severe COVID-19 receiving remdesivir treatment.