A simple microscope FTIR mapping method is illustrated for studying anisotropic diusion in zeolite. This method is based on measurements of evolution of the adsorbate concentration (IR absorbance) pro®les in two principal directions of a single zeolite crystal particle of a few ten microns in sizes. A mathematical model is presented and a comparison of its numerical solution with experimental data allows the determination of the diusivity in each direction in zeolite crystals. Diusion rates during desorption of n-hexane, n-octane and p-xylene in silicalite particles of 130 50 ´50 lm were experimentally studied with the microscope FTIR line mapping. Negligible changes in adsorbate concentration pro®les were observed after the silicalite particle saturated with one of the three hydrocarbons was exposed to air for about 15±44 h at room temperature. Under vacuum conditions and at higher temperatures, the hexane concentration pro®les developed within about 0.5 h, from which the averaged diusivity of hexane in the a and b channels of silicalite was found 1X1 Â 10 À10 cm 2 /s (at 80°C), signi®cantly higher than that for the c direction. Due to the intergrown microstructure of the single silicalite particles studied in this work, unusual adsorbate concentration pro®les were observed in some cases. These results suggest that the adsorbate may diuse in or out of the single crystal particle through the intercrystallite gaps connected with the straight b channels of silicalite.