The presence of Cesium-137 (137Cs) in the environment after nuclear accidents at Chernobyl and Fukushima Daiichi raises many health issues for the surrounding populations chronically exposed through the food chain. Unlike previous in vivo studies that focused solely on male exposures, this experimental research aims to assess the biodistribution and dosimetry of low-dose 137Cs internal exposure in both male and female C57BL/6 mice. This study uses a previously established model for chronic ingestion of 137Cs, simulating various exposure scenarios. Male and female C57BL/6 mice were exposed to concentrations resembling those ingested daily by residents in contaminated areas (20 kBq/L), as well as 5- and 10-times higher concentrations, for either 6 or 24 weeks. Throughout this period, the animals were closely monitored to determine and quantify the 137Cs content and to calculate absorbed doses. After 6 or 24 weeks exposure to chronic 137Cs in drinking water at 500 kBq/L, 137Cs concentration varied according to the organs and the sex of the animals. Males showed a higher body burden of 137Cs compared to females, with significant differences observed as soon as day 11. As well, the organs showing the highest 137Cs concentrations were skeletal muscle in males and in females, with significant differences between males and females. Regarding excretion, it appears that the elimination of 137Cs through feces was similar in males and females. By contrast, female mice showed a higher rate of 137Cs urine excretion than males, thus explaining the lower body burden in females. The resulting absorbed doses, calculated using dose conversion factors provided by ICRP publication 108, showed that the absorbed dose is 1.85 times less in female mice compared to male mice. 36.1 mGy in females and 66.9 mGy in males after 6 weeks exposure. 182.0 mGy in females and 310.0 mGy in males after 24 weeks exposure. This study demonstrates for the first time, sexual dimorphism in 137Cs biokinetics between males and females. These findings could refine biokinetic models of cesium and absorbed dose estimations in case of internal contamination, especially in post-accidental situations.