A reversed-phase liquid chromatographic method was developed for the quantitative determination of six triterpenoids, namely ganoderic acids C2, B, AM1, K, H and D in Ganoderma lucidum and its related species. Samples were extracted with chloroform in ultrasonic bath. The optimal conditions of separation and detection were achieved on an Agilent Zorbax SB-C18 column (250 mmx4.6 mm, 5 microm), with a linear gradient of acetonitrile and 0.03% aqueous phosphoric acid (v/v), at a flow rate of 1.0 ml/min, detected at 252 nm. All calibration curves showed good linearity (r2>0.999) within test ranges. The relative deviation of this method was less than 2% for intra- and inter-day assays, and the percentage recovery of the method was 93-103%, with relative standard deviation (R.S.D.) less than 5%. The current assay method was applied to quantitative determination of constituents of triterpenoids in 36 different samples of G. lucidum and its related species. The results indicated that the developed method could be readily utilized as a quality control method for G. lucidum and related species.