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, including a compound represented by the following formula (I) (wherein each of R1 and R2, which are identical to or different from each other, represents a saturated or unsaturated hydrocarbon group; R3 represents a C1-6 alkyl group or a C1-6 hydroxyalkyl group; m is an integer from 1 to 10; and X represents a halogen atom), and a phospholipid.