[Objective] This research was to establish a method for the determination of alpha-mangostin in Garcinia mangostana L. [Method] Reverse phase high-performance liquid chromatography(RP-HPLC) method with an ultra-violet detector(UVD) was performed on a 5 μm DiamonsilTM C18 column(250.0 mm×4.6 mm) at 25 ℃, the mobile phase composition was methanol-water(83∶17), the flow rate was at 1.0 ml/min, the detection wavelength was 317 nm. [Result] The method fulfilled all the standard requirements of precision, accuracy and linearity(r>0.999). The recovery was 98.9%, RSD was 1.87%. Alpha-mangostin contents of three batches samples of G. mangostana were 36.4, 37.3, 38.5 mg/g respectively, the average content was 37.4 mg/g. [Conclusion] RP-HPLC-UVD method is simple, accurate, high sensitivity, good reproducibility, and can be used for the determination of alpha-mangostin in G. mangostana. [Objective] This research was to establish a method for the determination of alpha-mangostin in Garcinia mangostana L. [Method] Reverse phase high-performance liquid chromatography (RP-HPLC) method with an ultra-violet detector (UVD) was performed on The mobile phase composition was methanol-water (83:17), the flow rate was at 1.0 ml / min, the detection wavelength was 317 nm. [Result The method fulfilled all the standard requirements of precision, accuracy and linearity (r> 0.999). The recovery was 98.9%, RSD was 1.87%. Alpha-mangostin contents of three batches samples of G. mangostana were 36.4, 37.3, 38.5 mg The average content was 37.4 mg / g. [Conclusion] RP-HPLC-UVD method is simple, accurate, high sensitivity, good reproducibility, and can be used for the determination of alpha-mangostin in G. mangostana.