Abstract: The cyclic peptides inPseudostellariae Radix were analyzed by ultra performance liquid chromatography-electrospray ionization time-of-flight-tandem mass spectrometry (UPLC-TOF MS/MS).Eleven cyclic peptides in PseudostellariaeRadix were separated by a reversed-phase C18 column using gradient eluteconditions. With the help of information dependent acquisition (IDA) mode anddynamic background subtraction (DBS), the interference of background ion waseliminated, and the MS/MS spectraogram of 11 cyclic peptides and accuratemolecular mass were acquired.