Objectives: Acute kidney injury (AKI) in patients hospitalized with COVID-19 has now been recognized as an important complication. Previous studies have shown that AKI in COVID-19 is associated with increase mortality. We aimed to investigate the difference in prognosis according to the timing and stage of AKI in patients with COVID-19. Methods: Patients hospitalized for COVID-19 at a dedicated COVID-19 hospital (Bagae hospital) were retrospectively collected from 2020 to 2021. Patients who developed AKI were identified and classified according to time-to-onset and stage. The hazard ratio (HR) of mortality outcomes was measured using Cox proportional hazard model after adjustment of multiple covariates.  Results: Out of 763 cases screened, AKI occurred in 218 (29%) cases. Among them, 85 patients developed AKI after hospitalization, and the other 133 cases were retrospectively diagnosed with AKI showing recovery trend after hospitalization. AKI was associated with worse survival outcome than the nonoccurrence (HR, 4.140 [1.407–12.181]). Depending on the time of occurrence, in-hospital AKI was independently associated with worse survival outcome. (HR,3.587 [1.093–11.769]). Age (HR,1.040 [1.019–1.061]), systolic blood pressure (HR, 0.988 [0.978–0.999]), underlying chronic kidney disease (HR, 3.251 [1.739–6.080]) and LDH (HR 1.002 (1.001–1.003)) were found as risk factors of in-hospital AKI. Additionally, in the analysis according to stage, it was associated with an increase in mortality from stage 2. (HR, 3.447 [1.093-11.769])   Conclusions: AKI in hospitalized patients with COVID-19 is associated with increased mortality. Compared with AKI that occurred before hospitalization, in-hospital AKI had a significant effect on patient outcome. Also, there was a positive correlation between the severity of AKI and mortality risk.