The present invention discloses humanized monoclonal antibodies that specifically bind to STn carbohydrate antigen with high specificity and selectivity, functional fragments of the humanized monoclonal antibodies such as scFv, conjugates and chimeric antigen receptors comprising the humanized monoclonal antibodies or the fragment thereof such as scFv. The invention further provides cells and compositions comprising the antibodies, fragments thereof or CARs as well as their use in diagnostics and treatment of cancer.