A pot experiment was carried out to study the effect of spraying exogenous substances YCL2 and Z5 after topping on the nicotine content,enzymatic activity of arginine decarboxylase and ornithine decarboxylase regulating the metabolism of nicotine,and total nitrogen,total sugar,chlorine,potassium.The results showed that spraying YCL2 and Z5 could significantly reduce the nicotine content with few influence on the other chemical qualities.With application of exogenous substance reducing the activity of arginine decarboxylase and ornithine decarboxylase,YCL2 decreased nicotine content by 20.47% in upper leaves,and Z5 decreased 34.36% and 32.38% in upper and middle leaves,respectively.It indicated that the effect of spraying YCL2 and Z5 on reducing nicotine content may be significantly related with its roles in decreasing the activity of arginine decarboxylase and ornithine decarboxylase.It would be one potential pathway to control nocotine content in burley tobacco production.