The concentrations of outdoor airborne bacteria measured in Seoul, Korea for one year (Jan. 2008~Dec. 2008) ranged from $500CFU/m^3$ to $7,500CFU/m^3$. In monthly concentration distribution, the level of outdoor airborne bacteria was highest in September and October and lowest in March. In seasonal concentration distribution, the order of level of outdoor airborne bacteria was autumn>winter>spring>summer. In regional concentration distribution, the highest level of outdoor airborne bacteria was generally found in the forest, followed by general area and traffic site. In distribution characteristics according to particle size, outdoor airborne bacteria showed 31% for >$7.0{mu}m$ (stage 1), 21% for $4.7{sim}7.0{mu}m$(stage 2), 15% for $3.3{sim}4.7{mu}m$(stage 3), 19% for $2.1{sim}3.3{mu}m$(stage 4), 10% for $1.1{sim}2.1{mu}m$(stage 5), and 4% for $0.65{sim}1.1{mu}m$(stage 6) and its mean respirable fraction was 48%. In concentration distribution by yellow dust, the mean levels of outdoor airborne bacteria were 803 $(pm479)CFU/m^3$ for period of yellow dust and 691 $(pm1,134)CFU/m^3$ for period of non-yellow dust. Although the level of outdoor airborne bacteria was higher in period of yellow dust than period of non-yellow dust, there was no significant difference between period of yellow dust and non-yellow dust (p>0.05). In correlation analysis between outdoor airborne bacteria and atmospheric factors (temperature and relative humidity), there was no significant correlation between outdoor airborne bacteria and atmospheric factors. The predominant airborne bacteria were identified to the Bacillus-derived species.