A cyclodextrin-based supramolecular hydrogel system with supramolecularly anchored active cationic copolymer/plasmid DNA (pDNA) polyplexes was studied as a sustained gene delivery carrier. A few biodegradable triblock copolymers of methoxy-poly(ethylene glycol)-b-poly-(epsilon-caprolactone)-b-poly[2-(dimethylamino)ethyl methacrylate] (MPEG-PCL-PDMAEMA) with well-defined cationic block lengths were prepared to condense pDNA. The MPEG-PCL-PDMAEMA copolymers exhibit good ability to condense pDNA into 275-405 nm polyplexes with hydrophilic MPEG in the outer corona. The MPEG corona imparted greater stability to the pDNA polyplexes and also served as an anchoring segment when the pDNA polyplexes were encapsulated in alpha-CD-based supramolecular polypseudorotaxane hydrogels. More interestingly, the resultant hydrogels were able to sustain release of pDNA up to 6 days. The pDNA was released in the form of polyplex nanoparticles as it was bound electrostatically to the cationic segment of the MPEG-PCL-PDMAEMA copolymers. The bioactivity of the released pDNA polyplexes at various durations was further investigated. Protein expression level of pDNA polyplexes released over the durations was comparable to that of freshly prepared PEI polyplexes. Being thixotropic and easily prepared without using organic solvent, this supramolecular in situ gelling system has immense potential as an injectable carrier for sustained gene delivery.