Recombinant Anti-HER2 x Anti-HER3 Bispecific Antibody (Bi-nanobody) is designed to be expressed as a VHH from anti-HER2 antibody variable domains fused with a VHH from an anti-HER3 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 and inactivate two receptors simultaneously. It is designed for the research of Breast cancer; Gastric cancer; Prostate cacncer; Ovarian cancer; Solid tumors therapy.