Background. Under count is a common phenomenon in health systems. One of the methods used for sensitivity identification of care system or identification of cases in registry is capture recapture method. Using two resources, this study aimed to estimate the actual mortality rates of under five-year-old children. Methods. This study was conducted by capture-recapture method (two resources), using the recorded data in death cause systems of the Iranian Ministry of Health and Medical Education (MOHME) and Treatment and Registry Office. The population included all children aged five years in Tabriz, Iran. We also considered all the death cases in the target population from 2020.03.20 to 2021.03.20. The death cases were extracted from two resources and entered into the Microsoft Excel software. After removing duplicate cases with a special formula, we obtained the actual mortality rates using capture-recapture method with 95% confidence interval (CI) and estimated the actual mortality rates and death cases. Results. In 2020, the death rate of under five-year-old children was calculated to be 344 cases (338 to 350 with 95% CI). The sensitivity rate of causal registry system for all death cases in the target population was 43.17%. Also, the mortality rate of under one-year-old children was calculated as 275 cases (271 to 280 with 95% CI). While the sensitivity rate of causal death for the mortality of under one-year-old children was 92.72%, it was 82.28% for the Registry Office. Conclusion. A combination of different software for death information registry and the registration of information in the occurrence location could be efficient techniques to reduce under count registrations. It is believed that better and more reliable information could be obtained on death case numbers through using two lists and capture-recapture method compared to using one of the two resources.