The present invention relates to immunology, biotechnology and medicine, notably to the field of antitumor pharmaceuticals based on monoclonal antibodies, and can be used in medicine for the treatment of oncological diseases.The object of the invention was to create an efficient and safe universal antitumor agent, the production of which effective, quick and easy. This problem is solved by the proposed humanized monoclonal antibody specific to syndecan-1, of the IgG4 isotype, or with IgG3 fragments and amino acid substitutions for the increase the antibody half-life, characterized by a definite combination of the calculated and created by the authors amino acid and nucleotide sequences, which is used as a self-acting substance for the therapy of tumor diseases. Nucleotide sequences additionally contain a fragment coding for a signal secretory sequence at the N-terminus, and are codon-optimized to increase antibody production in mammalian cells.