Endo-1,4-β-mannanases have a wide range of potential industrial applications. It was mainly used for the production of functional oligosaccharides in the food industry. In order to increase the production of endo-1,4-β-mannanases, inducible and constitutive expression of a novel endo-1,4-β-mannanase from Bacillus subtilis WD23 in Pichia pastoris GS115 was performed and the recombinant enzyme was characterized. The recombinant mannanase gene was successfully expressed in a fully active form in P. pastoris GS115, and the activity of recombinant mannanase reached to 5,156.742 U/mL, which was higher than those from other recombinant system. Optimal purified enzyme activity was detected at pH 6.3 and 70 °C, and the purified enzyme displayed broad temperature stability (40–70 °C). 150 mg/mL NaCl could still improve the activity of the enzyme. Flight mass spectrometry determination confirmed that recombinant proteins are mannanase.