B-Cell activating factor (BAFF) is critical for B cell survival and maturation; excessive expression of it corrupts B-cell tolerance and may lead to autoimmunity. The gene, scFv-Fc, coding for the antibody of BAFF was inserted into the eukaryotic expression vector, pPICZ alpha A, and transformed into Pichia pastoris. A high-level expression strain was obtained using a 'yeastern blotting' method. The scFv-Fc antibody was purified and 56 mg was obtained from 1 l of culture supernatant. It retained high binding activity to both soluble BAFF and membrane-bound BAFF.