Abstract: In order to investigate the effects of packet material on the moisture retentivity of cigarettes in an opened packet, the differences of isothermal moisture absorption properties among three kinds of cigarette packets (soft packet, soft-hard packet and hard packet) were investigated, and the differences of moisture loss rate of the same cigarettes in the opened packets of the three kinds were studied. The results showed that:1) The moisture absorption isotherms of the three kinds of packet materials differed significantly, their moisture adsorption properties increased with the increase of grammage of packet materials. 2) The effects of packet materials on the moisture loss rate of cigarette differed, the moisture loss rate of the same cigarette was the lowest in hard packet and the highest in soft packet. 3) In the process of moisture loss of cigarettes in a packet, there was an interaction of moisture between cigarette and packet material, which delayed the moisture loss rate of cigarette; and the isothermal moisture retentivity properties of packet materials affected the said interaction.