Immunoconjugates composed of mouse monoclonal antibody and anticancer drug was applied for the treatment of patients with colorectal cancer. Administration of mouse antibody raised human anti-mouse antibody that may interfere with the effect of immunoconjugates. To resolve this problem, human/mouse chimeric antibody was prepared and immunoconjugate of chimeric antibody and anticancer drug was developed. The characteristics of this new immunoconjugate were described.