[Objective] Endo β-1,4-mannanases play important roles in hydrolysis of the β-1,4 glycosidic linkages in mannans and heteromannans, the second most abundant hemicellulosic polysaccharides in nature. [Methods] In this study, we overexpressed and characterized an endo β-1,4-mannanase from Aspergillus nidulans in Pichia pastoris. [Results] A β-1,4-mannanase was successfully overexpressed in flasks and fermentor, and the yield of overexpressed protein in fermentor reached 3.90 mg/mL. The optimal pH and temperature of the enzyme were 4.0 and 60 respectively, and it was very stable over the pH ranges from 5.0 to 9.0. It was thermally stable below 40, whereas it was inactivated very quickly above 60. Its enzyme activities could be enhanced by Co²⁺ and Zn²⁺, whereas it was inhibited by Pb²⁺, Mn²⁺ and Cu²⁺. [Conclusion] This endo-β-1,4-mannanase could be well produced by Pichia pastoris, and has a potential as commercial enzymes for application.