Abstract: To investigate the effect of different concentrations of ozone on the internal quality of tobacco leaves, lower tobacco leaves were used as the experimental material and treated by different concentrations of ozone. Sensory evaluation, conventional chemical components determination and aroma components determination were carried out. The sensory evaluation showed that smoking quality of tobacco leaves was improved after different ozone concentration treatments. The effect of high ozone concentration (403.86 mg/L) was the optimal, with better smoothness of smoke, less offensive taste, and moderate strength. After tobacco leaves were treated by high concentrations of ozone, tobacco aroma components were more abundant, the types and contents of the aroma components were changed, and 19 kinds of new flavor components were generated, overall aroma effect was good. The contents of acids, alcohols and aldehydes esters also reached the highest value. The contents of total sugar and reducing sugar in the three groups were higher than that in the control group. After treated with high concentration of ozone, the contents of water-soluble total sugar, reducing sugar and sugar/nicotine ratio in the tobacco leaves reached the highest values. Based on the above-mentioned results, after treated by high concentration of ozone, the quality of tobacco smoke, the chemical and aroma quality of tobacco leaves were the best among different treatments.