Disclosed is an isolated monoclonal antibody or antigen-binding fragment thereof that specifically binds ErbB3, wherein the antibody or antigen-binding fragment interacts with amino acids 345-367 of SEQ ID NO:498, amino acids 423-439 of SEQ ID NO:498; and amino acids 451-463 of SEQ ID NO:498, as determined by hydrogen/deuterium exchange, wherein the sequences are as defined in the complete specification. Also disclosed is use of the antibody for inhibiting or attenuating tumour growth.