There are two rivers (Torii River and Kusu River) in the Togakushi Highland (Nagano Prefecture), in central Japan. Aquatic insects of those rivers were studied in August 1963. The results are summarized as follows : Torii River had more standing crops of aquatic insects than Kusu River, for. example the standing crop of station 3 (in Torii River) was 5.2g per 0.25m^2 in a wet sample. The net-spinners were dominant in Torii River, the communities of the river being in climax in the succession of aquatic insect communities of the rapids. In Kusu River, more creepers were found and standing crops were less than those of Torii River, the aquatic insect communities being far from the climax in the succession. Distribution of the net-spinning species of the two rivers are shown in Table 3.