The purpose of this study is to determine concentrations and compositions of $PM_{2.5}$ and their characteristic variations at Ieodo Ocean Research Station in the East China Sea and to examine the influence of air pollutants transported from Asia continents. $O_3$ and meteorological parameters were measured since June 2003 and $PM_{2.5}$ filter samples were collected from June 2004 to June 2008. In total, 244 samples were analyzed for water soluble ions and carbonaceous compounds. The mean mass concentration of $PM_{2.5}$ and $O_3$ were $21.8{pm}14.9{mu}g/m^3$ and $51.6{pm}16.1$ ppb, respectively. The average concentrations (mass fractions) of sulfate and ammonium were $6.26{mu}g/m^3$ (28.74%) and $1.59{mu}g/m^3$ (7.31%), respectively. Nitrate was considered to be lost through evaporation due to long stay at the station. The mean concentrations of EC and OC were $1.01{mu}g/m^3$ and $2.34{mu}g/m^3$, respectively, from June 2006 to June 2008. The average OC/EC ratio was 2.31. The organic matter converted from OC by multiplying 2.1 and elemental carbon constituted 22.60% and 4.66% of $PM_{2.5}$ mass, respectively.