Background Recent data have reinforced the concept of a reciprocal relationship between COVID-19 and kidney function. However, most studies have focused on the effect of COVID-19 on kidney function, whereas data regarding kidney function on the COVID-19 prognosis is scarce. Therefore, in this study, we aimed to investigate the association between eGFR on admission and the mortality rate of COVID-19. Methods We recruited 336 adult consecutive patients (male 57.1%, mean age 55.0 ±15.9) that were hospitalized with the diagnosis of COVID-19 in the tertiary care university hospital. Data were collected from the electronic health records of the hospital. On admission, eGFR was calculated using the CKD-EPI formula. Acute kidney injury was defined according to the KDIGO criteria. Binary logistic regression and Cox regression analyses were used to assess the relationship between eGFR on admission and in-hospital mortality of COVID-19. Results Baseline eGFR was under 60 mL/min/1.73m2 in 61 patients (18.2%). Acute kidney injury occurred in 29.1% of the patients. In-hospital mortality was calculated as 12.8%. Age-adjusted and multivariate logistic regression analysis (p:0.005, odds ratio:0.974, CI:0.956-0.992) showed that baseline eGFR was independently associated with mortality. Additionally, age-adjusted Cox regression analysis revealed a higher mortality rate in patients with an eGFR under 60 mL/min/1.73m2. Conclusions On admission eGFR seems to be a prognostic marker for mortality in patients with COVID-19; We recommend to determine eGFR in all patients on admission and use it as an additional tool for risk stratification. Close follow-up should be warranted in patients with reduced eGFR.