Abstract: A total of 214 tobacco leaf samples were systematically collected in two major tobacco-planting regions of Guizhou province to determine the relationships between tobacco leaf chemical components and quality at different scales. The results indicated that differences in chemical components,quality indicators and smoking quality were bigger among different counties than among different prefectures.At the county scale,major chemical components influencing leaf quality were rather similar,with the first principal component including total sugar,reductive sugar,nicotine,reductive sugar to nicotine ratio and total nitrogen to nicotine ratio.One or two principal components(or factors) can be used to evaluate tobacco leaf quality.At the prefecture scale,the relationship became complicated between chemical components and leaf quality,and more chemical components were needed to evaluate leaf quality.For example,significant correlation in Zunyi prefecture was found between smoking total scores and total nitrogen,nitrogen to nicotine ratio and nicotine,and between offensive odor and total nitrogen and chloride.At the provincial scale,the relationship was more complicated so that overall quality could be represented by using many more chemical components(including carbohydrates,compounds containing nitrogen,ratio and mineral nutrients).For example,significant correlation was found between total scores and total nitrogen,reductive sugar to nicotine ratio,nitrogen to nicotine ratio,phosphorous and magnesium,and between the offensive odor and total nitrogen,reductive sugar to nicotine ratio,nitrogen to nicotine ratio,phosphorous,magnesium and reductive sugar.It was concluded that more chemical components were needed to evaluate tobacco leaf quality at prefecture and provincial scales than at county scale.