Monosaccharides play important roles in biological processes. Sensitive and accurate analyses of monosaccharides remain challenging because of their high hydrophilicities and poor ionization efficiencies. Here, we developed a paired derivatization approach with H/D-labeled hydroxylamines for simultaneous quantification of 12 monosaccharides by liquid chromatography tandem mass spectrometry (LC-MS/MS). O-(4-Methoxybenzyl)hydroxylamine hydrochloride (4-MOBHA·HCl) showed higher derivatization efficiency for monosaccharides compared to six other hydroxylamine analogues. The derivatization of monosaccharides was readily achieved in an aqueous solution. Furthermore, the deuterium-labeled isotope reagent, d3-4-MOBHA·HCl, was newly synthesized to stably label monosaccharides to improve its accuracy and precision in complex matrix analysis. As a result, 12 monosaccharides were rapidly detected by LC-MS/MS within 16 min with significant improvements in chromatographic separation and retention time. The detection sensitivity increased by 83 to 1600-fold with limits of quantitation ranging from 0.25 to 3.00 fmol. With the paired derivatization strategy, the monosaccharides could be accurately quantified with good linearity (R2 > 0.99) and satisfactory accuracy (recoveries: 85-110%). Using this method, we achieved sensitive and accurate quantification of the monosaccharide composition of herbal polysaccharides and the change in monosaccharide levels in human cell lines under physiopathological conditions. More importantly, the developed method was able to differentiate between the levels of the monosaccharides in fecal samples of human ulcerative colitis (UC) patients and UC mice compared to their respective controls. The differential monosaccharides determined in human feces provided a good diagnostic performance in distinguishing the UC patients from healthy individuals, showing potential for clinical application.