A novel 2-(dimethylamino)ethyl methacrylate-block-2-(methacryloyloxyethyl phosphorylcholine) (DMAEMA-MPC) diblock copolymer was synthesized and investigated as a new non-viral vector for gene delivery. The attractive perspective of this phosphorylcholine (PC)-based material is its propensity to condense DNA efficiently via the cationic DMAEMA block, as previously demonstrated for the respective homopolymer, with the MPC block acting as a biocompatible steric stabilizer. Two series of DMAEMA-MPC diblock copolymers were synthesized for evaluation, varying independently and systematically either MPC or DMAEMA block length. Markedly different DNA-copolymer complexes were observed depending on the copolymer molecular composition. Certain polymeric structures led to formation of highly condensed, sterically stabilized DNA complexes of 120-140 nm diameter, while some resulted in partly condensed DNA-polymer complexes with 'spaghetti' structures, indicating the importance of a copolymer composition to balance condensing and steric stabilization effect. A low level of non-specific cellular association of the complexes with optimized physicochemical properties was seen, indicating the role of MPC surface layer in the interactions with biological membranes and important property in preventing promiscuous interactions with tissues in the body and potentially allowing for cellular specific delivery of the condensates following the attachment of a targeting ligand.