The dose distributions of high energy electron are perturbated strongly in regions of tissue inhomogeneity. The situation is quite complicated and, although the absorption of electrons is primarily determined by the number of electrons per gram which is almost constant for all materials, scattering depends strongly upon atomic number. Since the dose at any point is determined by the dose from the primary beam plus the dose from the scattered electrons, the absorbed dose will be different in materials of different density. The dose distribution is also dependent upon the range of the electrons which is inversely proportional to the density of the irradiated body when Z/A is virtually constant and the atomic numbers do not radically differ. In treatment planning, it is serious problems that the perturbations of dose distribution about the regions of inhomogeneous tissue, air cavities, lung, bone in body. Using the equivalent materials of inhomogeneous tissues, we measured the do e distribution from theses and calculated the correction factor“mean coefficient of equivalent thickness”and analyzed the preturbation of dose distribution. 1. For the inhomogeneities, appropriate correction of the dose distribution could be made by considering the“mean coefficient of equivalent thickness, <F>”of the materials as following. <FL=0.5 for lung> <FSB>=1.1 for spongy bone <FCB>=1.8 for compact bone <FA=0> for air cavity The isodoses were shifted towards the entry surface if <F> ＞1 and towards greater depths if <F>＜1. 2. Within and beyond tissues of lower density, such as lung, the decrease in attenuation resulted in an increase of the absorbed dose, and the dercease in scattering partially offset the elevation in dose. 3. The magnitude of the actual dose in and beyond low density regions, relatived to that on a unit denstiy basis, depended in a nonlinear manner on the location, extent, and density of the inhomogeneous region. 4. Within high atomic number material, s ch as bone, and immediately beyond in the interface region, there was an elevated dose, due to enhanced scattering. 5. The perturbation of dose distribution adjacent to cavities had shown that the percentage of dose increase varied markedly as a function of the buile-up layer, the length and thickness of the cavities, and the electron energy.