[en] The main sources of radon concentration in buildings are the underground surrounding soil and bedrock, construction materials and underground water supply. However, the contribution from these sources to the indoor radon level depends on many factors, such as type of the building, geology and pedology of the site and also the floor level. Focusing on this concern, the present work outlines on the characterization of the radon concentration in two different kinds of buildings - slab-on-grade dwellings and apartments on the second floor and above - in the Metropolitan Region of Belo Horizonte, Brazil, which is located in a large part on granite embasement area, the Granitic Gnaissic Complex. The radon concentration in dwellings and apartments, measured by using E-PERM Electrets Ion Chamber, ranged from 18.5 to 1591.0 Bqm^-3 (mean value 114.7 ± 5.5 Bqm^-3) and 3.7 to 185.0 Bqm^-3 (mean value 70.3 ± 6.7 Bqm^-3), respectively. Thus, the highest radon concentration is present in dwellings not in apartments, suggesting that the enhanced radon concentration maybe was originated mainly from local geological settings instead of other sources. In order to confirm this hypothesis, the measurements of the soil gas radon concentration were carried out by using AlphaGUARD PQ2000PRO detector and ²²⁶Ra (²¹⁴Bi) and ²²⁴Ra (²¹²Pb) specific activity in construction materials were determined by using gamma-ray spectrometry HPGe detector. These results confirmed the local geological setting as the main radon source. Moreover, radon concentration much higher than United States Environmental Protection Agency USEPA action level 148Bq.m^-3 occurred only in slab-on-grade dwellings. (author)