The viscosity of ethanol-water at various temperatures was determined. The physicochemical properties and characters of the solvents used as the mobile phase of reversed-phase high performance liquid chromatography(RP-HPLC) were compared between methanol and ethanol. The components of several Chinese medicines have been determined by RP-HPLC with ethanol-water used as mobile phase, and the results were compared with those obtained with methanol-water or acetonitrile-water. It showed that ethanol can be used as RP-HPLC mobile phase by increasing the column temperature moderately.