The thermal springs of Onikobe lie about 10km apart from the Narugo spa and are situated from the ravine of the river Araogawa to half-way up Mt. Araodake. There are 9 spas as shown in the maps consisting of more than 30 sources of thermal water, namely Miyazawa (common salt), Hukiage (salt geyser), Benten (geyser), Todoroki (simple), Kanizawa (earthy), Mitaki (common salt), Akazawa (sulphur), Araya (sulphur) and Megema-Ogama (geyser). Our investigation was undertaken in August, 1939. As we saw springs which remained in quite natural state, we could fortunately observe many sorts of algae that have grown abundantly. We have found in these hot springs 47 plants: 2 genera, 4 species of Bacteria (also “Schwefelrasen”), 21 genera, 29 species, 5 varieties, 1 form of Cyanophyceae, 1 genus, 1 species of Heterocontae, 2 genera, 2 species of Chlorophyceae, 2 genera, 4 species of Conjugatae. Moreover, 7 species of Cyanophyceae, 2 species of Chlorophyceae, 1 species of Conjugatae have been not yet identified. In these plants Mastigocladus laminosus is most frequently observed. Members newly known to the thermal flora of Japan are follows: Cyanophyceae: 10 species and 1 variety…Gloeocapsa punctata, Chroococcus bituminosus, C. minimus, C. varius, Synechocystis minuscula, Xenococcus Schousboei, Calothrix marchina var. crassa, Plectonema nostocorum, Nostoc punctatum, Anabaena thermalis, Lyngbya polysiphoniae. Heterocontae: 1 species… Tribonema aequalis. Chlorophyceae: 2 species… Gloeocystis vesiculosa, Microspora Wittrock. Conjugatae: 4 species.…Netrium oblongum, Cosmarium Ralfsii, C. rectosporum, C. granulatum.