A pharmaceutical composition includes a block copolymer having a hydrophilic segment, a hydrophobic segment, and a boronic acid compound bound to a side chain of the hydrophobic segment via a linker moiety that includes a heterocyclic structure. The heterocyclic structure contains a cyclic skeleton that includes a boron atom of the boronic acid compound, one or two atom(s) X bound to the boron atom and selected from an oxygen atom and a nitrogen atom, and one or two carbon atom(s) (respectively) bound to the atom(s) X. The block copolymer further includes at least one organic group bound to the carbon atom(s). The organic group(s) contain(s) an aromatic group or cyclic alkyl group that sterically protects a boronic acid ester bond and/or a boron amide bond resulting from bonding between the boron atom and the atom(s) X.