Inonotus obliquus could be isolated from Betula platyphylla var. japonica with diameter in the range of 6~13 cm that artificially inoculated by the fungus. The diameter and/or inoculation point of tree did not show any significant relationships with the infection rate of the fungus. Inonotus obliquus showed rapid growth on vertical direction of the infected tree while the growth was quite low on radial direction. The isolated fungus from the infected tree did not show vegetative incompatibility with the original fungus used for inoculation. We could isolate 8 contaminants from the inoculated area; Trichoderma reesei, T. atroviride, Cryptococcus neoformans, Botrytis cinerea, Fusarium sp. and 3 unknown species.