Abstract: This study was aimed to identify the photodegradation impurities(PD1 and PD2)in melphalan hydrochloride and establish a method for determining PD1 and PD2. The structures of the photodegradation impurities were inferred by LC-MS/MS. The impurities were confirmed by comparing with synthesized impurities. An HILIC method was established to determine PD1 and PD2. The method was carried out on an Atlantis HILIC column(4. 6 mm×150 mm, 3 μm)with the mobile phase consisting of 0. 1 mol/L ammonium formate(adjusted to pH 3. 0 with formic acid)and acetonitrile(13∶87)at the flow rate of 1. 0 mL/min. The column temperature was 35 °C. The detection wavelength was 260 nm. PD1 and PD2 were characterized as 4-amino-L-phenylalanine hydrochloride and 4-(2-chloroethyl)amino-L-phenylalanine hydrochloride, respectively. Melphalan hydrochloride, PD1 and PD2 were separated completely under the HILIC condition. The established HILIC method can be used to determine the photodegradation impurities.