The present invention provides a pharmaceutical composition. The pharmaceutical composition of the present invention is a pharmaceutical composition containing a block copolymer having a hydrophilic segment a hydrophobic segment and a boron compound linked to the side chain of the hydrophobic segment via a linker portion that includes a heterocyclic structure. The cyclic skeleton of the heterocycle has boron atoms derived from the boron compound atoms (X) selected from oxygen and nitrogen atoms that bond with the boron atoms and carbon atoms that bond with the atom (X) and the block copolymer further has organic groups that bond with the carbon atoms and contains aromatic groups or cyclic alkyl groups wherein the organic groups protect the boronic acid ester bonds and/or boron amide bonds attributed to the bonding of the boron atoms and the atoms (X).
