The chemical compositions of representative volcanic hot springs in the Kusatsu-Shirane volcano and the fluctuations in the contents of chemical components over 50 years are summarized. Although most hot springs are acidic, apparent differences exist in the chemical compositions of the hot springs located on the east and west sides of the Kusatsu-Shirane volcano. In the eastern hot springs (Kusatsu hot springs), a relatively simple formation model assuming the dilution of Cl-SO4-type hydrothermal fluids with surface water is applicable. In the western hot springs (Manza hot springs), hot springs with various water chemistries exist within a relatively small area, and the mixing of Cl-SO4-type hydrothermal fluids and SO4-rich shallow water emanating from H2S-rich vapor is considered responsible for the diversity in the chemical composition. The diversity of the Manza hot springs can be observed in the REE composition of rare earth elements, suggesting the involvement of secondary sulfate minerals in the shallow hydrothermal system. The formation of these secondary minerals is considered a factor in the diversity of water chemistry. The formation and dissolution of alunite and alkali metal-REEs double sulfates as its precursor, which selectively incorporates light-REEs (LREE), result in hot springs with diverse REE patterns in the Manza hot springs. Also, arsenic provides essential information for understanding the hydrothermal system. Two opposite types of hot springs can be found in the area: one with no H2S, high As concentration with a positive correlation to Fe concentration, and the other with significant H2S content, low As concentration with an inverse correlation to Fe concentration. Each type reflects the local hydrothermal systems involving the dissolution and precipitation of Fe-S-As minerals, respectively. In addition, the volcanic hot springs around the Kusatsu-Shirane volcano show compositional changes that reflect the rise and fall of volcanic activity, contributing to the monitoring of volcanic activity at the volcano. However, observations tailored to the characteristics of each hot spring source are necessary for volcanic activity assessment because the dissolved components that change with increasing volcanic activity differ from one hot spring source to another. In the case of three high-temperature hot spring sources, Bandaiko, Manza-Karafuki, and Manza-Yubatake, fluctuations in Na and Cl concentrations show good agreement with the rise and fall of volcanic activity. In the case of the Kagusa hot springs near the summit, the concentration of most dissolved components increases with the increase in Cl concentration in Yugama, an active crater lake, and Al, Fe, and K are particularly pronounced in the cations.