PM10 and PM2.5 in ambient air were collected in Seongbuk-gu area of Seoul for one year, from April 2005 to February 2006, and the concentration of PM-bound mercury was monitored. The annual concentrations of particles were 66.4±43.2 ㎍/㎥ (47.6±19.1 ㎍/㎥~106.1±78.0 ㎍/㎥) in PM10 and 37.2±20.4 ㎍/㎥ (28.0±23.4 ㎍/㎥~42.7±21.4 ㎍/㎥) in PM2.5, which is about 56% of PM10 concentration. The annual average concentrations of mercury were 0.125±0.078 ng/㎥ in PM10 and 0.141 ±0.080 ng/㎥ in PM2.5, respectively. In April of Asian dust season in Korea, mercury showed the highest concentration in both PM10 and PM2.5.