Recombinant Anti-DKK1 x Anti-SOST Bispecific Antibody (scFv4-Ig) is an appended IgG format, which includes four scFv moieties at the N-termini of the constant regions. It is a bivalent homodimer, in which one anti-DKK1 scFv is fused to the CH1 domain of a heavy chain and another anti-SOST scFv to the CL domain of a light chain, or vice versa. The resulting leads to 2+2 antigen-binding valency. This BsAb can bind two factors simultaneously and promote osteoblastogenesis. It is designed for the research of Osteoporosis; Osteogenesis imperfecta (OI); Low bone mineral density; Fracture therapy.