A DDS carrier enabling sustained release of a drug and a production method therefor. Wherein, the drug is retained by a PEG-carboxy group-containing polymer graft. Among polymers, a carboxy group-containing polysaccharide can be suitably used. The PEG-carboxy group-containing polymer graft is a compound prepared by grafting PEG into the carboxy group-containing polysaccharide. When the carboxy group-containing polysaccharide is used, it can be produced by utilizing a condensation reaction of an aminated PEG and a carboxy group-containing polysaccharide in coexistence with a triazine-based condensing agent. Alternatively, the PEG-carboxy group-containing polysaccharide graft can be produced by utilizing a condensation reaction of PEG and a carboxy group-containing polysaccharide in coexistence with an acid.
