1. Soil algal vegetaions in the certain radioactive districts in Japan are researched by means of crude cultures of soil samples.
2. The examined soils are obtained from a grassy plain in Ningyotoge, Tottori Prefecture (Na-1, Nb-1, Nd-1, -2, -3, Ne-1) and the experimental γ-irradiated field in Ohmiya, Ibaragi Prefecture (γ-R12, γ-R21, γ-10, γ-20, γ-30, . . . . . . γ-100) .
3. Thirty species of Chlorophyceae, five of Xanthophyceae, six of Bacillariophyceae, three of Cyanophyceae and one of Euglenophyceae are recognized from the soils of Ningyotoge, and fifty species of Chlorophyceae, two of Xanthophyceae, five of Bacillariophyceae, and six of Cyanophyceae are recognized from the soils of γ-irradiated field.
4. It seems that there is scarcely any differences on the algal composition of soil communities of unusual radioactive districts and of another usual districts.
5. In quantitatively, the soil algal micro-vegetaions researched in this study are dominately occupied by several cyanophycean members such as Phormidium tenue (MENEGH.) GOM., Nostoc punctiforme (KUETZ.) HARIOT, and Nostoc paludosum KUETZ.
6. A list of soil algae recognized in α-and γ-irradiated fields is given.