Abstract: In industrial fermentation processes,Saccharomyces cerevisiae is commonly used for ethanol production,but 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 Arabidopsis thaliana XI exhibited high specific XI activity (0.51 U/mg protein) in S.cerevisiae.The A. thaliana XI has low sequence similarities (50; -53; ) to the XIs previously functionally expressed in S.cerevisiae.The Km of the A.thaliana XI is 46.08 mM.Importantly,the A.thaliana XI is less inhibited by xylitol ( Ki,13.21mM),a side product during xylose fermentation.This work provides a promising starting point for further improvement of xylose fermentation in yeast strains.