OBJECTIVE： To establish a method for the determination of related substances in lorcaserin hydrochloride. METHODS： HPLC method was adopted. The determination was performed on Welch ultimate XB-ODS column with mobile phase consisted of Sodium dihydrogen phosphate（pH＝6.5）-acetonitrile （gradient elution） at the flow rate of 1.0 mL/min. The detection wavelength was set at 220 nm， and column temperature was 35 ℃. The sample size was 20 μL. RESULTS： The linear ranges of impurity 1， 2， 3 were 0.075 60-7.560 μg/mL（r＝0.999 9）， 0.081 40-8.140 μg/mL（r＝0.999 9）， 0.099 24-9.924 μg/mL（r＝0.999 9）， respectively. The limits of quantification were 0.075 60， 0.081 40， 0.099 25 μg/mL. The limits of detection were 0.022 68， 0.024 42， 0.029 77 μg/mL. RSD of precision test was lower than 2.0％. Impurity 1 was found in stability test and reproducibility test，RSD＜2.0％. The recoveries were 98.53％-102.45％（RSD＝1.06％，n＝9）， 98.26％-101.64％（RSD＝1.03％，n＝9）， 100.08％-102.10％（RSD＝0.70％，n＝9）， respectively. CONCLUSIONS： The method is sensitive， rapid， accurate and reliable， which can be used to determine the related substances of lorcaserin hydrochloride.