Abstract: A short term study of the chemical composition of rainwater was carried out from April to September 2005 at Yunfu city in Guangdong province. The major ions are SO42 for anions and Ca2+ for cations, with mean volume weight concentrations of 291.71eq/L and 284.65eq/L, respectively, both of which accounts for 75% to the total ion concentration. The SO42-/NO3- ratio was 8.64, indicating the sulfate was the major pollution matter. The cation Ca2+ appears to play significant role in neutralizing the acidity rainwater. Moreover, the higher ion concentrations are found in the transitional period between the flood seasons, and the lower ones in flood seasons. Except the NH4+, similar temporal variation was shown among other ions, suggesting they have the common source and similar transport channel.