Gene delivery is now a part of the therapeutic arsenal for vaccination and treatments of inherited or acquired diseases. Polymers represent an opportunity to develop new synthetic vectors for gene transfer, with a prerequisite of improved delivery and reduced toxicity compared to existing polymers. Here, the synthesis in a two‐step's procedure of linear poly(ethylenimine‐ b‐ 2‐isopropyl‐2‐oxazoline) block copolymers with the linear polyethylenimine ( l PEI) block of various molar masses is reported; the molar mass of the poly(2‐isopropyl‐2‐oxazoline) (PiPrOx) block has been set to 7 kg mol −1 . Plasmid DNA condensation is successfully achieved, and in vitro transfection efficiency of the copolymers is at least comparable to that obtained with the l PEI of same molar mass. l PEI‐ b ‐PiPrOx block copolymers are however less cytotoxic than their linear counterparts. PiPrOx can be a good alternative to PEG which is often used in drug delivery systems. The grafting of histidine moieties on the l PEI block of l PEI‐ b ‐PiPrOx does not provide any real improvement of the transfection efficiency. A weak DNA condensation is observed, due to increased steric hindrance along the l PEI backbone. The low cytotoxicity of l PEI‐ b ‐PiPrOx makes this family a good candidate for future gene delivery developments.