An immunoconjugate includes an anti-Globo H antibody, or a binding fragment thereof, and a therapeutic agent or a label, having the formula: Ab−(L−D)m, wherein Ab is the anti-Globo H antibody or the binding fragment thereof, L is a linker or a direct bond, D is the therapeutic agent or the label, and m is an integer from 1 to 8. The antibody may be a monoclonal antibody, which may be a humanized antibody. A method for treating a cancer includes administering to a subject in need of such treatment a pharmaceutically effective amount of an immunoconjugate containing an antibody against Globo H, or a binding fragment thereof, and a therapeutic agent covalently conjugated with the antibody.