Abstract: The article proposed a "micro-dissolution-welding" strategy tailored for microfibrillar cellulose (MFC). MFC was "micro-dissolved" in Urea/NaOH solution and the MFC fibers were "welded" together in coagulation bath, resulting in the formation of an MFC/lignosulfonate composite membrane. The mechanical properties, swelling behavior, and proton transport properties of this composite membrane in moisture environment were investigated. The mechanical strength and the the young's modulus of the resultant MFC/lignosulfonate composite membrane are 3.7±0.2 MPa and 58.6±3.9 MPa, respectively. The water absorption and planer swelling ratio of the composite membrane in water are (82±1)% and (13±2)%, respectively. The proton conductivity of the composite membrane at 80 ℃ reaches 0.056 S/cm, and its methanol permeability coefficient is 2.86×10^-6 cm²/s. The proposed "micro-dissolution-welding" strategy has promising applications in the field of cellulose-based functional membranes.