The research area is located in Pariangan, Tanah Datar, West Sumatera Province. The purpose of this study is to determine the geothermal system in Pariangan based on hydrothermal alteration and fluid geochemistry (hot springs). The lithology of research area is dominated by andesitic-basaltic lava and pyroclastic rocks (Quaternary). Surface manifestation of geothermal activity such as hot springs, warm springs and alteration minerals are identified in research area. Type of alteration developed in research area are dominated by argillic type characterized by the presence of illite, kaolinite, montmorilonite, dickite, and halloysite; propylitic type characterized by the presence of chlorite, epidote and, quartz; and phyllic type characterized by the presence of sericite, quartz, and chlorite. The result of fluids geochemistry analysis-concludes that all fluids classified as bicarbonate water which indicated volcano-magmatic environment source and has been mixing with meteoric water, thus suspected outflow zone of geothermal system. Based on analysis of conductive quartz geothermometer, estimated reservoir temperature ranges from 166 to 168°C and classified as moderate temperature geothermal system.