Abstract:The ratio of NH+4\|N /NO-3\|N and natural 15N abundance of NH+4 (δ15 NH+4) in rainfall in Hangzhou of Zhejiang province, China was determined between June 2003 and July 2005 using customized manual rainwater sampler. Our measurements indicated a similar seasonal variation in the NH+4\|N/NO-3\|N ratio and δ15NH+4 value in rainfall; peaks of NH+4\|N/NO-3\|N ratio in rainfall occurred when the farmland received fertilizers, followed by gradual decline to a lower level when the crop was harvested or the fertilizer application was terminated. In contrary, the δ15NH+4 value stayed negative when N-substances were applied to the crop, and then turned to positive when the crop was harvested or field was in fallow. Both NH+4\|N/NO-3\|N ratio and δ15NH+4 value in rain precipitation were evidently correlated with the chemical nitrogen fertilizer application during various crop growth stages, the alternation of seasonal transitions, and NH3 volatilization from other NH3 emission sources. Therefore, they could be regarded as an indicator in determining the sources, forms and composition of N in atmospheric wet deposition as well as the intensity of various NH3 emission sources from the land.