The anthocyanin compositions in red onion were analyzed using high performance liquid chromatography(HPLC)equipped with a diode array detector(DAD)combined with UV-Vis spectra and electrospray ionization tandem mass spectrometry(ESI-MS2).The pigments were extracted from red onion with 0.1% HCl(v/v)methanol solution,purified by an Amberlite XAD-7 column and characterized by means of HPLC-DAD-ESI-MS2 analysis.A total of 6 anthocyanins were identified from red onion according to the UV spectra,MS data and references.The sugars after the acid hydrolysis of anthocyanins were identified as glucose,and four were acylated.The major anthocyanins in the extracts were identified as cyanidin(Cy)-3-glucoside(26.43 %,peak area percent),Cy-3,5-diglucoside(9.38 %),Cy-3-malonyglucoside(37.27 %)and Cy-3,5-malonydiglucoside(12.57 %)respectively;two minor ones are peonidin(Pn)-3-malonyglucoside(8.60%)and Pn-3,5-malonydiglucoside(2.86 %).