A new HILIC-ELSD method was developed for compositional analysis of both xylo-oligosaccharides (XOS) with degree of polymerization (DP) from 2 to 8 and acetylated XOS with DP from 3 to 8. The method was carried out on a zwitterionic HILIC column using ELSD as a detector. The influences of mobile phase composition, column temperature and flow rate on the retention time and resolution of XOS were investigated. An excellent separation result was achieved with a linear gradient elution of 75%−50% acetonitrile in 30 min, at a flow rate of 1 mL/min and the column temperature at 35 °C. In addition, LC-ESI-MS was employed to determine the structural information of X7, X8 and acetylated XOS. The proposed method was simple, reliable, and no derivatization procedure was needed. It is suitable for compositional analysis and quality control of XOS.