The delivery of genetic materials to cells provides a promising treatment approach to many genetic diseases. The rational structural design for reducing the toxicity while improving transfection efficiency is an important strategy for the development of safe and highly efficient polycation gene vectors. In this study, a novel block copolymer composed of PEG and cationic histamine-like segments was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization and subsequently the potential of its gene vector was explored in vitro. The block copolymer showed a lower cytotoxicity to three cell lines. After complexation with pEGFP-C1, the resulting DNA-encapsulated micelles possessed uniform small size, high salt and serum tolerance which were confirmed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Highly efficient gene transfection was further obtained in human liver carcinoma (HepG2) in vitro. The low cytotoxicity and high transfection stem from the well-defined functions of different moieties, PEG segments, imidazolium and amine groups on histamine-like pendants contributing to the different steps of gene delivery, including colloid stability, highly effective DNA condensation and endosomal escape respectively.