Eleven tested anions were able to form adducts with neutral oligosaccharides at low cone voltage in negative ion mode electrospray mass spectrometry. Among them, fluoride and acetate have the abilities to significantly enhance the absolute abundance of [M-H]- for neutral oliogosaccharides. The chloride adduct has the best stability among all the adduct species investigated. For the above three anions, CID of adduct species may be used for structural determination of neutral oligosaccharides. In the presence of F- and Ac-, simultaneous detection of acidic oligosaccharides and neutral oligosaccharides was achieved. The ratio of Cl- : non-Cl-containing product ions obtained in CID spectra of chloride adducts of disaccharides was used to differentiate anomeric configurations of disaccharides. Density functional theory (DFT) was employed to evaluate the optimized structures of chloride adducts of disaccharides. The formation and decomposition of chloride adducts with oligosaccharides of different acidities were investigated in MALDI mass spectrometry.