Abstract: NH3 volatilization from the cultivated rice (Oryza sativa L.) canopy is one of the major contributing factors of the N loss in the rice production. The objectives of this study are to examine the genotypic variations in NH3 volatilization from canopy among the cultivars and to determine the mechanisms responsible for NH3 volatilization from rice. With these aims, two pot experiments were conducted using Yoshida culture solution and four rice genotypes (the Yangdao-6, the Wuyujing-3, the BG34-8 and the Zhenshan-97) in greenhouse at Huazhong Agricultural University, Wuhan City, China. The amount of ammonia volatilized from different rice cultivars was evaluated at booting, heading and milking stages. At booting stage, inhibitors of glutamine synthetase (methionine sulfoximine (MSO)) and photorespiration (isonicotinyl hydrazine (INH)) were sprayed on leaves at 0.1 mmol L-1 and 2 g L-1, respectively. Genotypic variations in amount of NH3 volatilized from canopy existed among the four rice cultivars at different growth stages and N treatments. According to results, spraying of the MSO at 0.1 mmol L-1 was significantly increased the NH3 volatilization from the rice canopy, while spraying INH at 2 g L-1 decreased the NH3 volatilization. Obtained results were showed that rate of ammonia volatilization was negatively correlated with the leaf GS activity, while the leaf GO activity related positively to the rice ammonia volatilization.