Abstract: The changes of diastase activity starch and reducing sugar of burley tobacco TN 86 during curing were studied.The results showed that the diastase activity and content of starch, soluble sugar and reducing sugar in tobacco leaves decreased with the advance of air-curing process and increased with the rise of stalk position, and their changes were correlated dynamically.The diastase activity reduced faster in the first 3-6 days during air-curing, somewhat later than the time when starch was rapidly decreasing, and there might be a positive correlation between their variation and moisture content of tobacco.The contents of starch, soluble sugar and reducing sugar in all stalk positions at the end of air curing were appropriate to quality burley tobacco.