Single inoculation method using a single resting spore of Plasmodiophora brassicae was developed. Single resting spore was obtained by placing a 0.5μl drop of spore suspension, which was adjusted to the concentration of 2000 spores per ml, on a piece of sterilized cover glass with a micropipette. The drop was checked under an inverted microscope to ensure that it exactly carried one spore alone. The cover glass carrying a single spore was placed on the surface of autoclaved soil in a pot. One- or two-day-old seedling of Chinese cabbage was inoculated by placing over the spore drop, covered with a small amount of soil, and grown in a growth chamber. The inoculation method could give an efficient infection. Pathogenicity of the single-spore isolates obtained was compared with their original populations to the host lines of European Clubroot Differential set, and was not always identical in those combinations.