Compensation of dose distribution of an electron beam for the oblique incidence is to shift the standardisodose curves according to the distance of the air space. The error of the corrected distribution from themeasured one was more than 10% when the space was more than 2cm in 8-12 MeV electron beam. The elelctron beamdiverged approximately in accordance with the inverse-square law when the scattering foil was assumed to be thevirtual source. Correction of the air space shifting and the inverse square law resulted in an error less than 3%.