The possibility of a gene carrier was investigated by in vitro transfection experiment with several cell lines. The poly(4-vinyl imidazole)(P4V) was synthesized by polymerization of 4-vinylimidazole (4V). The complex formation between P4V and DNA was confirmed by agarose gel electrophoresis and dye-exclusion assay. Using a light scattering spectrophotometer, particle sizes were determined. It was shown that The P4V/DNA complex exhibited very high transfection efficiency through the proton sponge mechanism of the imidazole groups with low cell toxicity.