This experiment was conducted during November in 2000 and February in 2001 in Taichung, central Taiwan. The study used a TE-PUF sampler, Universal air sampler and MOUDI (Micro-Orifice Uniform Deposit Impactor) sampler to collect the ambient air suspended particles and analyzed their water-soluble ions (Cl-, NO3-, SO42-, Na+, NH4+, K+, Mg2+ and Ca2+). Analytical results indicate that the mean mass concentration for PM2.5, PM2.5-10 and TSP measured at the CCRT (traffic) sampling site are 54.5, 27.8 and 158 μm/m3, respectively. Additionally, the mean mass concentration for PM2.5, PM2.5-10 and TSP measured at the THUC sampling site are 23.6, 16.3 and 85.6 μm/m3, respectively. Furthermore, the major water-soluble ion of PM2.5 measured in this sampling region are SO42- and NH4+, while those of PM2.5-10 are Cl-, NO3- and SO42-, respectively. At the CCRT (traffic) sampling site, the mean size distributions of mass, SO42- and NH4+ exhibit a bimodal distribution whereas those of Cl-, NO3-, Na+, K+, Mg2+ and Ca2+ have a bimodal distribution. At the THUC (campus) sampling site, the mean size distributions of mass, Cl-, NO3-, SO42- and Ca2+ are bimodal whereas those of Na+, NH4+, K+ and Mg2+ have display a unimodal distribution.