Abstract: The molecular structures and mechanism for the fragmentations of the related impurities were proposed by the MSⁿ and HRMS results obtained by high performance liquid chromatography-ultraviolet detector-fourier transform ion cyclotron resonace mass spectrometry(HPLC-UV-FTICRMS/MSⁿ). The molecular compositions of the related impurities and some of the fragmentations were confirmed by the HRMS datas. Four related impurities in puerarin bulk drug were separated. Their M+H⁺ ion peaks are m/z 433.112 95, 433.112 92, 417.118 01 and 417.118 01, respectively. They are identified as 3’-hydoxypuerarin, genistin-8-C-glucoside, neopuerarin B and neopuerarin A on the basis of fragmentation mechanism and reference data.