The aim of this master thesis is to investigatethe impact of the ventilation rate on radon concentration in an indoor environment.We wanted to determine whether the required quantities of freshair, prescribed or recommended by Slovenian legislation, are sufficient to ensure the concentration of radon in the limit values. For this purpose, we performed simulations using the CONTAM 3.2 software tool and verified the results with measurements already carried out in a bedroom located in the Idrija area. We also conducted a systematic review of studies on indoor air quality from the radon point of view and the potential impact of ventilation rate on radon indoor concentration. Based on the results of the research review, we have identified the potential impact of radon on human health. With the results of the master thesis, we concludedthat the provision of quality indoor air is necessary for users% health and comfort.The most often used minimum prescribed ventilation rate which,according to the Rules on ventilation and air-conditioning of buildingsequals 0,5 h-1, is not sufficient toensure indoor air quality. In areas with high radonexposure, a larger amount, depending on the intended use, should be considered for the kindergarten classroom and the office, which werethe subjects of my research. With the optimal amount of outdoor fresh air into the room, we ensure that radon concentrations remain below the limit of 300 Bq/m3, stated in the Decree on the National Radon Program,or below the recommended value of 100 Bq/m3, stated in the Slovenian standard SIST EN 16798-1: 2019. This also reduces the risk of negative health outcomes for users, whichmany studies have shown. Model verification and validation showed a match between 6% and 16%, depending on the selected month of the year. A major deviation occurs in October. We suggest efficient and constant ventilation of closed rooms, but at the same time,it is necessary to be aware that this is an immediate measureonly. In the case of high concentrations of radon, the problem must be solved entirely, that is,byananti-radon system. A complete risk prevention and management approach must be followed at all stages of construction of both new and refurbished facilities.