To provide a nucleic-acid-transfecting composition which exhibits low cytotoxicity, which facilitates a nucleic acid transfection into cells and which improves expression of the nucleic acid in the cells. The invention provides a composition for transfecting a nucleic acid into a cell and including a compound represented by the following formula (i) (wherein each of R 1 and R 2, which are identical to or different from each other and represents a C 12-22 saturated or unsaturated hydrocarbon group R 3 represents a C 1-6 alkyl group or a C 1-6 hydroxyalkyl group m is an integer from 1 to 10 and X represents a halogen atom), and a phospholipid.
