Abstract <p>The Kuril Islands stretch for more than 1200 km from the Kamchatka Peninsula to Hokkaido Island. This area hosts active Pleistocene to Quaternary volcanism with more 30 active volcanoes. The eight Kuril Islands (Paramushir, Shiashkotan, Rasshua, Yankich, Ketoy, Urup, Iturup and Kunashir) are marked by the presence of active volcanoes exhibiting solfatara and hydrothermal activity. Differences in volcanic evolution, hydrological and geological conditions have led to differences in the conditions of formation and discharge of thermal waters of the region. The hydrothermal features include low-temperature solfataras, water and water-mud pots of various shapes and sizes, thermal pools, springs within a broad temperature range. There are three main hydrochemical groups of thermal waters discharging on the islands. Acid sulfate waters (steam-heated waters) with temperatures up to 95°C and TDS up to 5 g/L are in thermal fields of most activity volcanoes. On slopes of the Ebeko (the Paramushir Island), Sinarka (the Shiashkotan Island), Berg (the Urup Island), Baranskiy (the Iturup Island), Mendeleyev and Golovnin (the Kunashir Island) volcanoes, there are hot springs with acid (pH &lt; 3) Cl–SO₄ (SO₄–Cl) waters with temperatures up to 80–85.5°C and a mineral content of up to 14 g/L. Along the coast of the Shiashkotan, Rasshua, Iturup and Kunashir islands, near-neutral chloride sodium waters with a mineral content of up to 12–16 g/L and temperatures of up to 90°С spring out. There are separate groups of springs that do not belong to any group.</p>