During storage of tobacco product, menthol is redistributed among the tobacco, filter and paper independently of the application method, and permeates through the wrapping material. Therefore, it is indispensable to develop an estimation method for the amount of menthol escaping from a pack during storage. When an investigation of the escape rate is undertaken, the phase / state of menthol has to be specified at first; namely, if menthol exists in the solid phase, the vapour pressure within a pack should be equal to the saturated vapour pressure, and the vapour pressure would remain constant until the solid-phase menthol within a pack disappears. However, if menthol exists in an adsorbed phase, the vapour pressure should be the equilibrium vapour pressure, and the pressure would decline with a decrease in the amount of adsorbed-phase menthol. Therefore, the phases of menthol on the tobacco and the filter were analyzed by DSC measurements. The results revealed that menthol was not deposited but adsorbed on them. This conclusion was confirmed by the fact that the measured menthol distribution within a pack of on-market product was in good agreement with one calculated using the binary adsorption equilibria of menthol and water on tobacco and filter, which had been measured in advance. In response to the above results, a mathematical model was developed which utilized the binary adsorption equilibrium relationship, the apparent diffusion coefficient through packed cigarettes, and the permeation coefficient of wrapping material. The apparent diffusion coefficients were measured, assuming that the packed cigarettes could be treated as a uniform packed bed of tobacco shred, and the permeation coefficient was measured by the steady-state transfer method. The calculated results of the menthol distribution inside a pack wrapped with paper were in sufficient agreement with the experimental ones. Therefore, the amount of menthol escaping from a pack wrapped with an arbitrary material could be estimated once its permeation coefficient is measured.