This study aims to establish a new method for quality evaluation of Gentianae Macrophyllae Radix by simultaneous determination of five iridoids (loganic acid, 6'-O-beta-D-glucopyranosylgentiopicroside, swertiamarin, gentiopicroside, sweroside), and to detect five iridoids in the root of eight species (Gentiana macrophylla, G. straminea, G. crassicaulis, G. dahurica, G. robusta, G. waltonii, G. lhassica, and G. tibetica). The separation was carried out on a Shiseido SPOLAR C18 (4.6 mm x 250 mm, 5 microm) column eluted with mobile phase of water containing 0.04% formic acid (A) and acetonitrile (B) in a gradient program. The flow rate was 0.8 mL x min(-1). The detect wavelength was set at 240 nm. The column temperature was kept at 30 degrees C. The volume of injection was 5 microL. The five iridoids were well separated with ideal linear correlations. The average recoveries were 97.35% - 106.23%. All the five iridoids were detected in the root of eight species. The contents of same species changed in a somewhat wider range. The contents in root of G. dahurica were lower than that in other species.