In this work, the regional deposition analysis of attached fraction of radon havernbeen studied. So as to find the regional deposition of the inhaled activity, a fortranrncode is used. The parameters and the assumptions used in the code were developedrnby ICRP. The regional deposition from modified parameters were compared withrnICRP model deposition. According to the comparison, it was observed that therndeposition of attached fraction in the lower (trachea-bronchial) regions of the respiratoryrntract was found small incontrast their deposition in the extrathoracic (ET) regionrnbecomes dominant as aerodynamic diameter of aerosols increases.rnxi