To understand the ionic and elemental components in PM2.5 over eastern coastal areas in China, aircraft measurements were carried out from 25 December, 2002 to 6 January, 2003. PM2.5 filter samples were collected and analyzed for mass concentrations, nine ionic components and 15 trace elements. The highest concentrations of PM2.5 were observed at the lowest altitudes, indicating the influence of ground-level sources. Sulfate, nitrate and ammonium were the main water-soluble components, and the sum of their concentrations accounted for 60–70% of the total ionic mass. Cl− depletion was observed to an extent of 3–26%. Anthropogenic ally derived particles contributed about 60% of the total measured ionic components, and natural sources such as sea salts and soil dusts contributed another 40%. Different to many earlier studies, Ca2+ was found to mainly originate from anthropogenic sources. PM2.5 showed an acidic nature, with a neutralization potential/acidic potential ratio of less than 1.0. NH4+ was the major neutralizer of aerosol acidity. A good correlation was observed between the concentrations of NO3− and nssCa2+, suggesting that photochemically produced HNO3 was partly absorbed by mineral particles. S had the highest concentrations among the 15 elements. The enrichment factor values of the observed elements were all over 1, indicating that all of them were influenced by anthropogenic sources. The enrichment factors of Pb, S, As, Cu and Zn were over 100, and suggesting that they were greatly enriched.