For cost-effective and efficient ethanol production from plant biomass, the conversion of not only hexose sugars, such as glucose, but also pentose sugars, such as xylose, is required.In industrial fermentation processes, Saccharomyces cerevisiae is commonly used for ethanol production.However, it lacks the ability to ferment pentose sugars like D-xylose.Heterologous expression of a xylose isomerase (Ⅺ) would enable yeast cells to metabolize xylose.However, many attempts to express a prokaryotic Ⅺ with high activity in S.cerevisiae have failed so far.The present work is on functionally expressing xylose isomerase (Ⅺ) of plant origin in Saccharomyces cerevisiae.The Hordeum vulgare Ⅺ exhibited high specific Ⅺ activity (0.54 U/mg protein) in S.cerevisiae.The H.vulgare Ⅺ has low sequence similarities (50-53%) to the Ⅺs previously functionally expressed in S.cerevisiae.The Km of the H.vulgare Ⅺ is 40.17 mM.Importantly, the H.vulgare Ⅺ is less inhibited by xylitol (Ki, 18.33 mM), a side product during xylose fermentation.This work provides a promising starting point for further improvement of xylose fermentation in yeast strains.