Adequate retention in blood circulation is a prerequisite for construction of gene delivery carriers for systemic applications. The stability of gene carriers in the bloodstream requires them to effectively resist protein adsorption and maintain small size in the bloodstream avoiding dissociation, aggregation, and nuclease digestion under salty and proteinous medium. Herein, a mixture of two block catiomers consisting of the same cationic block, poly{N-[N-(2-aminoethyl)-2-aminoethyl]aspartamide} (PAsp(DET)), but varying shell-forming blocks, poly[2-(2-methoxyethoxy) ethyl methacrylate] (PMEO(2)MA), and poly[oligo(ethylene glycol) methyl ether methacrylate] (POEGMA), was used to complex with plasmid DNA (pDNA) to fabricate polyplex micelles with mixed shells (MPMs) at 20 degrees C. The thermoresponsive property of PMEO(2)MA allows distinct phase transition from hydrophilic to hydrophobic by increasing incubation temperature from 20 to 37 degrees C, which results in a distinct heterogeneous corona containing hydrophilic and hydrophobic regions at the surface of the MPMs. Subsequent study verified that this transition promoted further condensation of pDNA, thereby giving rise to improved complex and colloidal stability. The proposed system has shown remarkable stability in salty and proteinous solution and superior tolerance to nuclease degradation. As compared with polyplex micelles formed from single POEGMA-b-PAsp(DET) block copolymer, in vivo circulation experiments in the bloodstream further confirmed that the retention time of MPMs was prolonged significantly. Moreover, the proposed system exhibited remarkably high cell transfection activity especially at low N/P ratios and negligible cytotoxicity and thus portends promising utility for systemic gene therapy applications.