The present invention relates to a block copolymer for overcoming drug resistance of tumours to chemotherapy, comprising blocks A and B, connected to each other with a hydrolytically, reductively or enzymatically biodegradable linker, wherein the hydrophilic block A is formed by poly(N-(2-hydroxypropyl) methacrylamide), eventually containing comonomers enabling covalent binding of drugs, and the hydrophobic block B is formed by a polypropylene oxide. The invention relates also to a polymer conjugate containing the block copolymer and the low molecular weight drug, to a pharmaceutical composition containing them and to the use thereof in medicine.