Abstract: In order to effectively control the nitrogen metabolism in overgrown tobacco plants at mature stage and promote the quality of flue-cured leaves, field trials were conducted between 2013-2014 to investigate the effects of an enzyme inhibitor, 4-hydroxyl(methyl)phosphinoyl-DL-homoalanine(glufosinate). The activities of nitrate reductase (NR) and glutamine synthetase (GS), key enzymes for nitrogen metabolism, and the chemical components in tobacco leaves were determined. In addition, sensory quality of treated flue-cured tobacco leaves for cigarettes was panel tested. The results showed that spraying the enzyme inhibitor at different concentrations at mature stage effectively decreased NR and GS activities in tobacco leaves, and the concentration of the enzyme inhibitor significantly negatively correlated to the NR and GS activities. The NR and GS activities declined quickly in the treated leaves and good field performance was achieved at the enzyme inhibitor concentrations between 10 and 15 mg/L. After spraying at the appropriate concentrations at mature stage, the contents of protein, nicotine and total nitrogen decreased, while those of reducing sugar and total sugar increased in the flue-cured leaves. The leaf chemical composition was more harmonious, the pigment content was reduced and the contents of neutral aroma components increased by 25.04%-42.76%. These have resulted in an increased score of sensory by 7.22%-10.43%. Considering cost and safety, 10 mg/L was recommended as a more appropriate concentration.