Abstract: The effect of GA₃(Gibberellic Acid:C₁₉H₂₂O₆) on the alkaloid content and composition in upper leaf was investigated with Yunyan 87 as experimental material,the results showed that:1) the contents of total alkaloid,nicotine,nornicotine,anatabine and anabasine significantly decreased by GA₃ spraying at the concentration of 1.5×10^-5-3.5×10^-5;2) the contents of total alkaloid,nicotine,nornicotine,anatabine and anabasine were significantly negatively correlated with GA₃ concentration in the range of 0 to 3.5×10^-5,the confidence level for anabasine was P<0.05 and for the others was P<0.01;3) with the increase of GA₃ concentration in the range of 0 to 35×10^-5,the percentage of nicotine in total alkaloid increased,while the percentages of nornicotine,anatabine and total microalkaloid decreased,and the percentage of anabasine changed little;4) in the range of 0 to 3.5×10^-5,the confidence level of correlation between the percentage of nicotine or total microalkaloid in total alkaloid and GA₃ concentration was P<0.01,and that of nornicotine or anatabine was P<0.05.The irritancy of upper leaf of flue-cured tobacco could be significantly weakened by GA₃ spraying at suitable concentration,and it was of benefit to the leaf quality.