Abstract: Acid deposition has caused severe environmental pollution in Nanshan area of Chongqing.The effect and harm of acid deposition on soil and vegetation of forest ecosystem were studied according to guidelines and technical manuals for acid deposition monitoring network in East Asia.It was found by soil analysis that the pH values of soil were low at 5 sampling sites with average value of 3 74 in Layer A and average value of 4.20 in Layer B.The average value of base cation saturation(BS) was less than 10%.The effective cation exchange capacity (CEC) ranged from 78.1 to 88.6 mmol/kg in Layer A and from 61.1 to 65.1 mmol/kg in Layer B.The high content of aluminum in soils of all the 5 sampling sites was possibly associated with the input of atmospheric S and N,which has led to acidification of soil and soil water.The C/N ration was low,at around 12.0 in Layer A and declining with the soil depth,which indicated that the organic matter was well decomposed under warm and rainy subtropical climate.According to vegetation analysis,acid deposition might do harm to fir and cryptomeria,both of which are acid sensitive.