A DDS carrier that allows the sustained release of a drug, and a method for producing the same. The present invention is characterized in that a drug is held in a PEG-carboxy-group-containing polymer graft. A carboxy-group-containing polysaccharide can be used suitably among the polymers. The PEG-carboxy-group-containing polymer graft is a compound in which polyethylene glycol is grafted to a carboxy-group-containing polymer. When a carboxy-group-containing polysaccharide is used, a polymer graft can be produced by utilizing a condensation reaction between aminated PEG and a carboxy-group-containing polysaccharide in the presence of a triazine condensing agent. A PEG-carboxy-group-containing polysaccharide graft can also be produced by utilizing a condensation reaction between PEG and a carboxy-group-containing polysaccharide in the presence of an acid.
