Abstract: The change of chemical components in moistered tobacco leaves with storage duration was studied.Two grades of Yunnan tobacco, B2F and C3F of cultivar K 326, were conditioned and then stored at ambient air temperature 40℃ and relative humidity 80% for 1, 2, 4, 16, and 24 hours, repectively.The contents of chemical components in the stored leaves were determined.The results showed that the contents of total sugar, nicotine, starch, nitrate, and total volatile base in the conditioned leaves were decreased with the lasting of storage duration, but the content of reducing sugar was on the contrary.It was concluded that the smoking quality of the conditioned leaves could significantly be improved by storage at suitable temperature and humidity for a proper length of time.