An isolated monoclonal antibody that specifically binds human OX40. A nucleic acid molecule encoding the antibody, an expression vector, a host cell and a method for expressing the antibody are also provided. The present invention further provides an immunoconjugate, a bispecific molecule, a chimeric antigen receptor, an oncolytic virus and a pharmaceutical composition comprising the antibody, as well as a treatment method using an anti-OX40 antibody of the invention.