Abstract ：Ammonia volatilization is an important way of nitrogen fertilizer loss in paddy field. Taihu Lake region, a typical intensive agricultural area in China, has become an important emission source due to its high N input. However, the effect of shift of rice cropping systems on ammonia emission, from traditional rice-wheat rotation to ratoon rice, is still lack of research in this area. The experiment was conducted to reveal the characteristics of ammonia emission from ratooning rice with two treatments, i.e. rice-wheat rotation (RW) and ratoon rice system (RR), in the Lake Tai watershed. The results showed that cumulative ammonia volatilization of RR was 74.3 kg/hm2, accounting for 17.9% of the total N applied. The main periods of ammonia volatilization loss were tillering fertilizer stage and regenerated tillering fertilizer stage, accounting for 31.2% and 27.0% of the total loss, respectively. The yield, ammonia emission intensity and partial factor productivity from applied nitrogen of RR were 14.1 t/hm2, 5.29 kg/t and 33.9 kg/kg. Compared with RW, ammonia volatilization accumulation, yield and nitrogen partial factor productivity of RR increased by 40.7%, 43.0% and 51.6%, respectively. Overall, our results indicated that the ratoon rice relative to rice-wheat rotation increased ammonia emission but produced higher grain yield and equivalent ammonia emission intensity, suggesting that there could be a great potential for ammonia volatilization reduction of ratooning rice in Taihu Lake Basin, which is needed further research.