The radon concentrations were measured to survey distribution of radon concentrations in Seoul subway stations. The radon concentrations in air and water were measured at seventeen subway stations(Mapo, Chungjongno, Sodaemun, Kwanghwamun, Chongno3ga, Ulchiro4ga, Tangdaemun, Sangildong on Line 5;Nowon, Chunggye, Hagye, Kongnung, Taenung, Mokkol, Chunghwa, Sangbong, Myomok on Line 7) using the $RAdtrak^{TM}$ radon gas detector, Pylon AB-5 continuous passive radon detector and liquid scintillation counting method from January to May 1999. The major results obtained from this study were as follows: The long-term mean concentrations of radon were $61.8;Bq/m^3$ in office, $78.9;Bq/m^3$ in platform, $38.2;Bq/m^3$ in concourse and $20.1;Bq/m^3$ in outdoor, respectively. These levels were less than the action level ($148;Bq/m^3$) of the U.S. EPA. The highest level of short-term mean concentrations was $116.55;Bq/m^3$ at Chongno3ga station on the 5th line subway stations, while the lowest mean concentration was $19.55;Bq/m^3$ at Mokkol station on the 7th line subway stations. The highest concentration of radon in the road water and storing underground water in the subway stations was $234.7;KBq/m^3;and;155.5;KBq/m^3$ in Sodaemun subway station, respectively. The results suggest that radon concentration in subway stations seems to be affected by ventilation and radon concentratin in underground water in the subway stations.