This study aims to clarify details of hydrothermal system in the Bandung volcanic basin (west Java, Indonesia), one of the richest geothermal resource areas in Indonesia, by hydrochemical methods. For this, hydrochemistry and stable isotope ratios of the water samples taken from the Bandung volcanic basin are analyzed and their differences between hydrothermal systems in the southern and northern parts of that area are revealed. Major ions, including several dissolved trace elements such as Li, B, F and As, were measured for the 19 samples collected from 10 hot springs, 1 crater, 4 springs, 3 wells and 1 surface water in the two regions. Hydrogen and oxygen isotope ratios were also used to identify the origin and hydrogeological process of the waters in each area. As the result, most hot springs in both the areas were found to be composed of immature waters in young hydrothermal systems while only 3 samples were classified as old hydrothermal waters. The southern part was characterized as the higher Li, B, F and As concentrations and the enrichment of oxygen 18 than those in the northern part. These differences suggest that the portion of deep thermal fluids of the hot springs in the southern part is higher than in the northern part. Another suggestion is advanced reaction between the rocks and hot waters in the southern part because of the higher reservoir temperature. Accordingly, the hydrochemical properties of the reservoir fluids is probably different between the two areas, which can serve bases to delineate the boundary of two areas, estimate water circulation patterns and assess geothermal resources by geothermometers using specific chemical elements.