A method for assaying a DDS compound containing a saccharide compound-modifi ed carboxy C1-4 alkyldextran polyalcohol and a drug compound residue bonded to this carboxy C1-4 alkyldextran polyalcohol, or a DDS compound wherein a polymer carrier is bonded to a drug compound residue via a spacer containing 2 to 8 amino acids bonded together via peptide bonds, which involves the step of assaying a hydrolysate obtained by treating the DDS compound with peptidase.
