Background Malnutrition is still a global public health problem contributing for under-five morbidity and mortality. Specifically, childhood mortality attributable to malnutrition is high at Felege-Hiwot Comprehensive Specialized Hospital. However, there is no recent evidence that shows the time to death and public health importance of oxygen saturation and chest in drawing in the hospital. Therefore, estimated time to death and its predictors can provide an input for program planners and decision-makers in the study area.Methods An institutional-based retrospective cohort study was conducted among 488 severe acute malnourished under-five children admitted from the 1st of January 2016 to the 30th of December 2019. The study participants were selected by using simple random sampling technique. Data were entered in to Epi-Data version 3.1 and exported to STATA version15 statistical software for further analysis. The Kaplan Meir was used to estimate cumulative survival probability and a log-rank test was used to compare the survival time between different categories of explanatory variables. The Cox-proportional hazard regression model was fitted to identify predictors of mortality. P-value < 0.05 was used to declare statistical significance.Results Out of the total 488 randomly selected charts of children with severe acute malnutrition, 476 records were included in the final analysis. A total of 54(11.34%) children died with an incidence rate of 9.1death /1000 person- days. Failed appetite test (AHR: 2.4; 95%CI: 1.26, 4.67), altered consciousness level at admission (AHR: 2.4; 95%CI: 1.08, 4.67), oxygen saturation below 90% (AHR: 3.3; 95%CI: 1.40, 7.87), edema (AHR 2.9; 95%CI: 1.45, 5.66) and HIV infection (AHR: 2.8; 95%CI: 1.24, 6.36) were predictors of mortality for children diagnosed with severe acute malnutrition.Conclusion The overall survival status of severe acute malnourished children was low as compared to national sphere standards and previous reports in the literature. The major predictors of mortality were oxygen saturation below 90%, altered consciousness, HIV infection, edema and failed appetite test. Therefore, early screening of complications, close follow up and regular monitoring of sever acute malnourished children might improve child survival rate.