The silver tin oxide powders were prepared by hydrothermal method using ammonia and citric acid as complex of silver ions, and oxalic acid, sulfuric acid and citric acid as reductant. The Ag-SnO2 composite powders were characterized by differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy(SEM) and energy spectrum analysis. The results show that the silver tin oxide composite powders could be synthesized in different hydrothermal systems. In the system with ammonia as complex of silver ions, sodium sulfuric and oxalic acid as reductant, respectively, silver and tin oxide deposit completely. In the system with sodium sulfuric as reductant, the prepared composite powder is mainly flake structure with about 300 nm thickness. While in the system with oxalic acid as reductant, the prepared composite powder is spherical structure with about 100 nm particle size. In the system with citric acid as both complex and reductant, the tin oxide do not deposit completely and the prepared composite powder is irregularly spherical particle with smaller size of about 30 nm