It is known that radon concentration is particularly great in regions with the heightened content of uranium in soil and water and with geological breaks of the earth crust. The Republic of Uzbekistan is located in granitoid zone. Concentration of radon in soil’s air varies from 1000 Bq/m3 in the west parts of the country up to 20,000 Bq/m3 in the submontane parts. And high concentration of radon gas is found in houses and underground structures all over the Uzbekistan. For example, the concentration of radon exceeds the regulation level 10-100 times in 14% of premises in Tashkent, in 41% in the city of Almalyk and 44% in the city of Yangyabad. The purpose of this work is creating a method to reduce concentration of radon gas in buildings and underground structures. The concentration of radon can be reduced by using polymeric compositions which fill pores inside the construction materials and decrease coefficient of permeation of radon atoms and water molecules in construction materials (concrete, gypsum, etc.). In the paper polymeric organic compounds are investigated and selected as the chemicals to prevent radon seeping indoors. Gas (air, Ar, 222Rn, H2O) permeability of concrete and gypsum after treatment by chemicals has been examined. Experiments have shown that chosen method of treatment of the construction materials allows reducing the coefficient of gas permeability in 200 – 400 times. The treatment of floor, walls and ceiling of 25 buildings’ basements has reduced the radon concentration in the premises of the first floor from 400 - 600 Bq/m3 to the background value of 17-20 Bq/m3.