Abstract: In order to investigate the effects of cigarette filter on the physical retention of moisture in cigarette, the isothermal moisture adsorption and moisture loss of the whole cigarette, tobacco rod and filter segment were separately studied. The differences in water activity between cigarette, tobacco rod and filter at the early stage of water loss, as well as their dehydration rates, were measured and analyzed from 21 cigarette samples of different specifications. The results showed that:there were significant differences between tobacco rods and filter segments regarding isothermal moisture adsorption and moisture loss. At the early stage of moisture loss of cigarette, the internal moisture migrated from the tobacco rod towards the filter segment, causing rapid moisture loss of the tobacco rod. This resulted in accelerated moisture loss and the reduction of moisture retention by the whole cigarette. The moisture loss rates of 21 cigarette samples were higher than those of their corresponding tobacco rods by 28.6% on average. These results indicated that improving the cigarette filter's physical retention of moisture and reducing the moisture migration from tobacco rod towards filter were beneficial to the promotion of physical retention of moisture in cigarette.