Ammonia volatilization losses,nitrogen utilization efficiency,and rice yields in response to urea application to a rice field were investigated in Wangzhuang Town,Changshu City,Jiangsu Province,China.The N fertilizer treatments,applied in triplicate,were 0 (control),100,200,300,or 350 kg N ha~(-1).After urea was applied to the surface water,a continuous airflow enclosure method was used to measure ammonia volatilization in the paddy field.Total N losses through ammonia volatilization generally increased with the N application rate,and the two higher N application rates (300 and 350 kg N ha~(-1)) showed a higher ratio of N lost through ammonia volatilization to applied N.Total ammonia loss by ammonia volatilization during the entire rice growth stage ranged from 9.0% to 16.7% of the applied N.Increasing the application rate generally decreased the ratio of N in the seed to N in the plant.For all N treatments,the nitrogen fertilizer utilization efficiency ranged from 30.9% to 45.9%.Surplus N with the highest N rate resulted in lodging of rice plants,a decreased rate of nitrogen fertilizer utilization,and reduced rice yields.Calculated from this experiment,the most economical N fertilizer application rate was 227 kg ha~(-1) for the type of paddy soil in the Taihu Lake region.However,recommending an appropriate N fertilizer application rate such that the plant growth is enhanced and ammonia loss is reduced could improve the N utilization efficiency of rice. Ammonia volatilization losses, nitrogen utilization efficiency, and rice yields in response to urea application to a rice field were investigated in Wangzhuang Town, Changshu City, Jiangsu Province, China. The N fertilizer treatments, applied in triplicate, were 0 (control), 100, 200, 300 , or 350 kg N ha ~ (-1). After urea was applied to the surface water, a continuous airflow enclosure method was used to measure ammonia volatilization in the paddy field. Total N losses through ammonia volatilization generally increased with the N application rate , and the two higher N application rates (300 and 350 kg N ha -1) showed a higher ratio of N lost through ammonia volatilization to applied N. Total ammonia loss by ammonia volatilization during the entire rice growth stage ranged from 9.0 % to 16.7% of the applied N. Increasing the application rate generally decreased the ratio of N in the seed to N in the plant. For all N treatments, the nitrogen fertilizer utilization efficiency ranged from 30.9% to 45.9%. Surpl us N with the highest N rate resulted in lodging of rice plants, a decreased rate of nitrogen fertilizer utilization, and reduced rice yields.Calculated from this experiment, the most economical N fertilizer application rate was 227 kg ha ~ (-1) for the type of paddy soil in the Taihu Lake region.However, recommending an appropriate N fertilizer application rate such that the plant growth is enhanced and ammonia loss is reduced could improve could improve the N utilization efficiency of rice.