Abstract: For investigating the effects of aging time on the main physical characteristics of microwave expanded stem during processing,the changes of moisture content,variation rate of volume during moistening,filling value and yield of expanded stem with aging time were studied,and the variation rate of whole volume was used to evaluate the variation degree of expanded stem volume during moistening.The results showed that with the prolongation of aging time,the variation rate of aging volume increased,while the variation rate of volume before and after moistening and that of whole volume decreased;the change rates diminished after 7 days,however the variance coefficient of whole volume variation rate was less than 10%.Aging time affected the filling value of expended tobacco stem granules to a certain extent,it affected the yield of product slightly.The proper aging time of microwave expanded stem was 7 to 14 days.