A novel hydrophilic interaction liquid chromatography coupled with tandem mass spectrometry (HILIC-MS/MS) method was developed for the simultaneous determination of 23 free amino acids without derivatization.The method was performed on an ultra-high performance liquid chromatography (UHPLC) separation system coupled with electrospray ionization mass spectrometry on a triple quadrupole mass spectrometer (TQ-MS),operating in positive ionization mode.Sufficient separation of the 23 underivatized amino acids was achieved on an Acquity BEH Amide column (2.1 mm × 100 mm,1.7 um) in a single run of 12 min at a flow rate of 0.4 mL min-1.The limits of detection were in the range from 0.17 to 77.75 ng mL-1.All the analytes were quantified directly from biological extracts without any kind of derivatization,which avoided the laborious and time-consuming of derivatization procedures used by the traditional method.Also,the more polar compounds were separated without utilization of perfluorinated acids as ion-pairing reagents which was not suggested for ESI source.Then,the method was applied for the analysis of the free amino acids in 46 batches of Ziziphus jujuba fruits which comprised 39 cultivars from 26 cultivation regions.Multivariate statistical analysis was also used to investigate the differences in free amino acid profiles among the samples.This study showed that HILIC-UHPLC-TQ-MS is an effective technique to analyze underivatized amino acids in the biological samples.