The present work was undertaken to derive a theoretical formula of mass transfer under a reduced pressure, especially the transition regime, through the gas kinetic-theory and compare it with the experimental results. The Maxwell moment method utilizing the two-sided Maxwellian distribution function having been proposed by Lees et al. was applied to the mass transfer between two concentric spheres. In the process of analysis, the accomodation coefficient for mass transfer was taken into account. The analytical solution in which the value of accomodation coefficient was evaluated as 0.9 showed in good agreement with the experimental results of sublimation of naphthalene
