The wave-like temperature and density distributions in snow under an applied temperature gradient, found by Sokratov and Maeno <1998>, were used to estimate the effective water vapor diffusion coefficient in snow. Values obtained were (0.6--2.0)¿10-5 m2 s-1, lower than the water vapor diffusion coefficient in air and much smaller than previous results found in the literature. The difference was discussed with the use of results of CO2 diffusion measurements in snow under an isothermal condition and the introduction of a new parameter, the gradient enhancement factor (f ). It was concluded that the effective water vapor diffusion coefficient of snow is dependent on the porosity, tortuosity (&tgr;), and gradient enhancement factor. The mean values of &tgr; and f were 1.73 and 2.3, respectively, for the snow studied. ¿ 2000 American Geophysical Union