The in door ra don be hav ior has com plex dy nam ics due to the in flu ence of the large num ber of dif fer ent pa ram e ters: the state of in door at mo sphere (tem per a ture, pres sure, and rel a tive humid ity), aero sol con cen tra tion, the ex change rate be tween in door and out door air, con struction ma te ri als, and liv ing hab its. As a re sult, in door ra don con cen tra tion shows vari a tion, with the usual pe ri od ic ity of one day and one year. It is well-known that sea sonal vari a tion of the ra don con cen tra tion ex ists. It is par tic u larly in ter est ing to in ves ti gate in door ra don vari ation at the same mea sur ing lo ca tion and time pe riod, each year, due to es ti ma tion of in di vid ual an nual dose from ra don ex po sure. The long-term in door ra don mea sure ments, in a typ i cal fam ily house in Ser bia, were per formed. Mea sure ments were taken dur ing 2014, 2015, and 2016, in Feb ru ary and July, each year. The fol low ing mea sur ing tech niques were used: ac tive and char coal can is ters meth ods. Anal y sis of the ob tained re sults, us ing multivariate anal y sis meth ods, is pre sented.