The size-fractionated inhalable particles in ambient air were collected at the top of a lab building in a university campus of Shanghai; F - , Cl - , NO 3 - , SO 4 2 - , and NH 4 + were extracted to determine the concentration. In every size, the concentration of the five ions followed the order of SO 4 2 - >NO 3 - ~NH 4 + ~Cl - >F - . Their concentrations in PM 1 . 6 were 5-7, 1-5, 3, 1-3, and ~0.1μg/m 3 , respectively, and occupied about 8-11%, 2-7%, ~6%, 2-6%, and ~0.1% of PM 1 . 6 mass, respectively. In PM 8 , about 70% of each ion existed in PM 1 . 6 , while in PM 3 . 7 , 50-80% was in PM 1 . 6 . The size distributions of SO 4 2 - , NO 3 - , Cl - , and F - were characterized by bimodal types with fine mode peaking around 0.7μm and coarse particle mode peaking around 3-5μm. NH 4 + showed a single fine mode peaking at 0.7μm. Fine mode dominated the size distribution of SO 4 2 - , NO 3 - , and NH 4 + . SO 4 2 - , NO 3 - , Cl - , and NH 4 + had a good correlation in PM 1 . 6 between each other. But SO 4 2 - strongly correlated to NO 3 - at every size stage. Comparison of size-fractionated equivalent ratios between [SO 4 2 - ] and [NH 4 + ] suggested that the existing forms of SO 4 2 - , NO 3 - , Cl - , and NH 4 + were probably (NH 4 ) 2 SO 4 , NH 4 NO 3 , and NH 4 Cl. [SO 4 2 - ]/[NO 3 - ] ratio in fine mode was >1, which revealed that stationary source emission was still the important contributor to fine particles. The main sources of particulate inorganic ions were also discussed.