A series of blend membranes were prepared from cellulose and konjac glucomannan (KGM) in NaOH/thiourea aqueous solution by coagulating with 5 wt.% CaCl2 aqueous solution. The miscibility, structure, water permeability and mechanical properties of the membranes were measured, and the effects of KGM content on the microporous formation, pore size and pore size distribution of the blend membranes were investigated. Fourier transform infrared spectroscopy, differential scanning calorimetry, scanning electron microscopy, wide-angle X-ray diffraction indicated that cellulose and KGM were miscible in the whole range of their weight ratios. The new crystalline plane formed due to the resemble structure and interaction between cellulose and KGM. With an increase of the KGM content, pore size (2r(f)) and water permeability (UFR) of the blend membranes rapidly increased, then reached a plateau of about 50 nm at w(KGM) greater than or equal to 30%. The tensile strength and breaking elongation in dry state for the blend membranes slightly decreased, and then significantly decreased at w(KGM) greater than or equal to 50%. The content of through pores of the cellulose membranes blended with KGM increased, and the pore size distribution became wider, compared with pure cellulose membrane. KGM plays an important role in the formation of through pores for the microporous membranes, leading to higher water permeability. Therefore, it provides a novel way to prepare the membrane and porous gel particles with various pore size for application in the separation field.