Exposure to natural sources of radiation including , andespecially radon and its short-term products, is an important issue around the world. Radon is a radioactive gas released from normal decay of radium element in rocks and soil. It typically moves up through the ground to the air above and into your home through cracks and other holes in the foundation. When radon gas is breathed in, it enters the lungs, exposing them to small amounts of radiation. This may damage the cells in the lining of the lungs and increase a person's risk of lung cancer. The determination of radon gas concentration in indoor places is very important because 65 to 95% of human life is spend in indoor places. Therefore, radon gas concentration in indoor places has been measured in many cities around the world, including Iran. By determining the concentration of radon gas in different places, we can reduce the damages caused by radon gas. In this project, we measure the concentration of radon gas in 8 Metro stations and 5 parkings and some houses in the city of Isfahan by using RTM1688. The measured values of radon gas in all places were less than 100 but the radon gas concentration in the basement of one of the houses was about 500 . So we collected the samples of building materials that were used in that place and by using HPGe detector, determined the radioactivity of samples to understand whether the high concentration of radon gas in this place is due to the radiation of the building materials used in it or not. The results showed that radioactivity of building materials used in the house were in the normal range, and therefore could not be the reason for high level of radon gas concentration in that place and perhaps the high level of radon gas is related to its geological position. Exposure to natural sources of radiation including , andespecially radon and its short-term products, is an important issue around the world. Radon is a radioactive gas released from the normal decay of the elements uranium and radium in rocks and soil. It typically moves up through the ground to the air above and into your home through cracks and other holes in the foundation. When radon gas is breathed in, it enters the lungs, exposing them to small amounts of radiation. This may damage the cells in the lining of the lungs and increase a person's risk of lung cancer. The determination of radon gas concentration in indoor places is very important because 65 to 95% of human life spend in indoor places. Therefore, radon gas concentration in indoor places has been measured in many cities around the world, including Iran. By determining the concentration of radon gas in different places we can reduce The damages caused by radon gas. In this project, we measure the concentration of radon gas in 20 points (houses, parkings and Metro stations (by using RTM1688-2. Then where the concentration of radon gas was high, we collect the samples of building material that used in this place and by using HPGe detector, determine the radioactivity of samples to understand whether the high concentration of radon gas in this place is due to the radiation of the building materials used in it or not?.