Submicron aerosol number concentration (N_CN) and the size distributions were measured in a continuous manner at Yonsei University located near the center of Seoul, South Korea, during 2004-2010. Cloud condensation nuclei number concentration at 0.6% supersaturation (N_CCN) was also measured during 2006-2010. The number of days with reliable measurement data was 787, 891 and 589 days, respectively. The N_CN, geometric mean diameter of aerosols (D_g) and N_CCN are in the range of 18094±7149 cm^-3, 49±10 nm, and 5272±3143 cm^-3. The average N_CCN is comparable to the one measured at an island about 200 km to the west of Seoul, which is a downwind region of Shandong Peninsula where Chinese industries are heavily located. Both N_CN and N_CCN had strong tendency to reach their daily minimum value between 3 and 5 AM throughout any time of the year. The values of N_CCN/N_CN and D_g tended to reach their daily maximum during these hours. N_CN and D_g showed strong positive and negative correlation (r² > 0.80), respectively, with the traffic amount at the major road about 500 m away from the instrument room. However, N_CCN showed much weaker correlation (r²<0.30). In terms of seasonal variation, the highest N_CN, N_CCN and N_CCN/N_CN were all found during winter and the lowest N_CCN, N_CN and N_CCN/N_CN during autumn. Between April and July, particle formation and growth events occurred in more than 10% of the total measurement days and the most frequent month was May with about 25%. On the other hand, the event was found less than 5% of the measurement days between December and January.