A reverse-phase high-performance liquid chromatographic method is developed for the determination of astragaloside IV, a characteristic constituent in Radix Astragali. Samples are analyzed by means of a reverse-phase column (Zorbax Eclipse XDB C18) using acetonitrile and water under gradient conditions as the mobile phase for 30 min. An evaporative light-scattering detector is used and set at an evaporating temperature of 43 degrees C with a nebulizing gas (compressed air) pressure of 3.4 bar. The detection limit (signal-to-noise ratio > 5) of astragaloside IV is 40 ng on-column.