beta-Mannanase is the key enzyme in the hydrolysis of mannan which has been widely applied in diverse industrial fields such as biobleaching pulps, food and feed industry, bioethanol and pharmaceutical applications. In this study, a novel GH5 family beta-mannanase gene (LrMan5B) with 381 amino acid residues was identified from Lichtheimia ramosa, and highly expressed in Pichia pastoris X33. The amino acid sequence shares the highest identity (64%) with the beta-mannanase from Rhizomucor miehei. Purified recombinant LrMan5B showed the optimal activity at pH 5.0 and 65 degrees C. It had broad-range pH stability (retaining > 65% activity after incubation at pH 3.0-8.0 at 37 degrees C for 24 h) and was highly thermostable (retaining > 80% activity after incubation at 60 degrees C for 30 min). LrMan5B displayed the highest catalytic efficiency for locust bean gum and the k(cat)/K-m value was 1357.47 mL.mg(-1).s(-1), followed by guar gum (512.82 mL.mg(-1).s(-1)), konjac glucomannan (454.21 mL.mg(-1).s(-1)), and palm kernel meal (137.00 mL.mg(-1).s(-1)). In order to evaluate the synergistic effect of LrMan5B and alpha-galactosidase LrAgal36A from L. ramosa, LrAgal36A was supplemented to hydrolyze palm kernel meal with LrMan5B together, showing that the reducing sugar release significantly increased by 21% (compared with the sum of that by hydrolysis of single Lrman5B or LrAgal36A). Due to its favorable enzymatic properties, LrMan5B might own potential applications in the area of food and feed processing.