Recombinant Anti-DKK1 x Anti-SOST Bispecific Antibody (Tandem scFv) is designed to be expressed as a scFv from an anti-DKK1 antibody variable domains fused with a scFv from an anti-SOST antibody variable domains. It contains a His-tag at the C/N terminus for affinity purification. The BsAb exits as monomer in reducing and non-reducing conditions. 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.