L-Rhamnose isomerase (L-RI) displays a great potential in biological production of various rare sugars because of its broad substrate specificity towards many aldoses and ketoses, including D-psicose and D-allose. The crystal structure of L-RI has been solved recently and its gene has been cloned, sequenced and high-level expressed. L-RI variant improved by molecular modification will be the dominant enzyme for industrial production of D-allose. Recent advances on crystallographic structure analysis and catalytic mechanism of various L-RIs were overviewed. Enzyme properties and application in D-allose production were also provided in detail, and the potential research trend of L-RI was prospected.