We aimed to investigate the relationship between air pollution and the Infant mortality rate (IMR) during nearly ten years in Tehran, Iran. This study is a retrospective cohort case using time series analysis. Air pollution monitoring data during the study period (2009-2018) were collected from the information of 23 Air Quality Control Centers in different areas of Tehran. For this purpose, the daily measures of PM10, PM2.5, O3, CO, SO2, NO2 were obtained. Data on infant mortality was obtained from the National Statistics Office of Iran and mortality registered in Tehran's main cemetery during the study period. Distributed lag linear and non-linear models were used. A total of 23,206 infant deaths were reported during the study period. Following an increase of 10 ug/m3 in PM10 in an early day of exposure, the risk of mortality increased significantly (RR=1.003, 95%CI:1.001-1.005). There is a pick on lag 5-10 that shows a very strong and immediate effect of cold temperature which means that cold temperatures increase the risk of mortality at an early time. At cold temperate, (var=0 and lag 0) risk of infant mortality was significantly higher than reference temperature (19°C) (RR=1.1295, %CI: 1.01-1.25). The results show the adverse effects of PM10 exposure on infant mortality in Tehran, Iran. Accordingly, a steady decline in PM10 levels in Tehran may have greater benefits in reducing the Infant mortality rate.