Background: Indoor levels of 222Rn in some residential areas in Ramsar are as high as 31, 000 Bq/m3, resulting in mean internal exposures up to 71 mSv/y. The main goal of this study was to develop a simple mathematical model for predicting radon concentrationfrom gamma radiation level in dwellings located in high background radiation areas (HBRAs) and a nearby normal background radiation area (NBRA) of Ramsar. Materials and Methods: The levels of gamma background radiation and indoor radon were measured in 350 dwellings located in normal and high background radiation areas (210 dwellings from HBRAs and 140 dwellings from NBRAs). Moreover, data about the most important environmental factors such as temperature and humidity as well as the inhabitants’ nutrition were collected. Results: The mathematical relationship between the gamma radiation level and indoor radon concentration in NBRAs and HBRAs is introduced in this study. The findings obtained in this study clearly indicate that in normal and high background radiation areas of Ramsar the majority of confounding factors such as the type of building materials and ventilation in different houses are almost identical. Therefore, the level of gamma radiation can be used as a strong predictive tool for radon concentration. Conclusion: As radon concentration in indoor air strongly varies with time, the simple mathematical methods developed in this study, can help health physicists and environmental scientists have an estimate of the mean radon level in these area.