D-Mannose has prebiotic effect and potential medical application. Besides, it can be used as substrate to produce mannitol, a functional polyol widely used in food industry. As this result, it has attracted many researchers' attention. In this work, a thermostable D-mannose-producing D-lyxose isomerase (D-LI) was characterized from a hyperthermophile, Thermosediminibacter oceani. The recombinant D-LI could be remarkably activated by Mn2+. It displayed maximal activity in presence of 1 mM Mn2+ at pH 6.5 and 65 degrees C, and was determined to be highly thermostable at 80 degrees C. The half-life was calculated to be 5.64, 2.82,0.77, and 0.2 hat 70, 75, 80, and 85 degrees C, respectively. The enzyme showed the optimum activity using D-lyxose as substrate and could also effectively catalyze the isomerization between n-fructose and D-mannose. Under optimum conditions, 101.6 D-mannose was produced from 400 D-fructose after reaction for 9 h, giving a conversion yield of 25.4%. (C) 2016 Elsevier Ltd. All rights reserved.