Purpose: Vitamin C is a well-known antioxidant and a few papers reported to improve symptoms and prognosis in sepsis and pneumonia. In this study, we studied the effect of vitamin C when used in viral pneumonia patients with severe respiratory failure. Methods: This is a single center, retrospective review study of patients admitted to the medical intensive care unit from January 2015 to April 2017. There were total 201 patients with viral pneumonia, among them 35 patients used vitamin C. We performed statistical analysis by matching age and baseline characteristics that statistically different of these patients. Results: The baseline characteristics of the patients had a few differences between vit c group and non-vit c group such as age (59.6 ± 14.8 vs. 65.9 ± 14.3, p=0.025), extracorporeal membrane oxygenation (ECMO) (28.6% vs. 5.4%, p<0.001) and procalcitonin ((5.4 ± 10.2 vs. 12.6 ± 27.4, p=0.039). The 28d mortality was no difference between two groups (20.0% vs. 24.7%, p=0.327). In matched group, the 28d mortality was not significant difference between two groups (20.0 % vs. 37.1 %, p=0.073). Besides shock reversal within 14days (45.7% vs. 31.4%, p=0.220) and recovery after acute kidney injury (52.9% vs. 55.6%, p=0.877) were also no different between two groups. Vitamin C was not prognostic factor for the mortality (p=0.334). Conclusion: Adjunctive intravenous vitamin C therapy alone did not reduce 28d mortality in patients with severe viral pneumonia with respiratory failure.