A novel design of a biodegradable carrier for drug delivery was established by constructing a supramolecular assembly of drugs and polymer backbones without any covalent bonds. A biodegradable polyrotaxane was synthesized in which alpha-cyclodextrins (alpha-CDs) as drug carriers were threaded onto poly(ethylene glycol) chains which then were capped at each chain end by L-phenylalanine via peptide linkages. The release of alpha-CDs was observed only when the terminal peptide linkages were degraded.