Background: Although antiretroviral therapy access for HIV infected children increased dramatically, anemia have been continued as a challenge regardless of cluster of differentiation (CD4) count and viral load. Hence, this study aimed to assess the time to detection of anemia and its predictors among children receiving antiretroviral therapy at Debre Tabor referral hospital and University of Gonder Compressive Specialized hospital, 2020.Methods: A retrospective follow-up study was conducted from January 2010 to December 2018. A total of 372 children under the age of 15 who had received ART were included in the study. Data were collected from children’s medical charts and ART registration logbook using a standard checklist. Besides, the data were entered into EPi data 4.2.2 and then exported to Stata 14.0 for further analysis. The Cox regression model, the variables having P-value ≤.05 with 95% CIs in multivariable analysis were declared as a statistically significant for anemia Result: The mean (±SD) of follow-up periods were 56.6 ±1.7 SD months. The overall median survival time free from anemia was 137 months, and the incidence rate of anemia was 6.9 per 100 PYO (95% CI: 5.3, 7.8). Moreover, WHO clinical staging of III/IV [AHR: 4.2, 95% CI: 1.80, 11.1], low CD4 count below threshold [AHR: 1.9, 95% CI: 1.09, 3.37], cotrimoxazole preventive therapy non-users, and poor level of adherence [(AHR: 2.4, 95% CI: 1.20, 4.85] were the main predictors of anemia. Conclusion: The incidence rate of anemia was found to be high. Monitor hemoglobin levels routinely with concurrently CD4 cell count levels, WHO clinical stage, and level of adherence. Hence, preventing and correcting of those predictors in a systematic manner in ongoing basis is crucial. Moreover, strategies need to be strengthened cotrimoxazole preventive therapy supplementation