Aim: COVID-19 is a lethal disease for which there is still no specific treatment. The study aims to retrospectively investigate the effect of adding lopinavir/ritonavir to the treatment of patients using favipiravir (in the ward or intensive care unit) on mortality. Methods: This study was conducted in 181 Rt-PCR(+) adult patients with severe and critical COVID-19. Demographic and laboratory data, antiviral agents used in treatment (with or without lopinavir-ritonavir), presence of intubation, and clinical outcome were recorded. The patients were categorized into Group 1 (not receiving lopinavir-ritonavir), Group 2 (administered lopinavir-ritonavir in ward), and Group 3 (administered lopinavir-ritonavir in the intensive care unit). Results: The lowest mortality rate was found with Group 2 (21.4%) while this rate was 77.9% for Group 3 and 42.3% for Group 1 (p<0.001). There was no significant difference in length of hospital stay among groups (p>0.05). While 35.2% (25 patients) of Group 1 needed intubation, this rate was 21.4% (9 patients) in Group 2 (p<0.001). Conclusions: This study demonstrated that lopinavir / ritonavir treatment reduced mortality and the need for intubation when initiated before the critical pneumonia phase. Lopinavir/ritonavir may be useful in the treatment of COVID-19, especially as part of the combination regimen.