A DDS compound comprising a carboxy(C_1-4)alkyldextran polyalcohol modified with a saccharide compound and a residue of drug compound bound to the carboxy(C_1-4)alkyldextran polyalcohol, and a method for measuring a DDS compound in which a polymer carrier and a residue of drug compound are bound to each other by means of a spacer comprising 2 to 8 amino acids linked by peptide bond(s), which comprises the steps of treating the DDS compound with a peptidase, and measuring the resulting hydrolysate.