Provided are a cationic lipid which facilitates the introduction of a nucleic acid into, for example, a cell or the like； a composition containing the cationic lipid and a nucleic acid； a method for introducing a nucleic acid into a cell by using a composition containing the cationic lipid and the nucleic acid； and the like. The cationic lipid is, for example, a cationic lipid represented by formula (A): formula (A): (wherein R 1 is alkenyl or the like, R 2 is alkenyl or the like, R 3 and R 9 are each alkyl, or are combined together to form alkylene, or R 3 and R 5 are combined together to form alkylene, R 5 is a hydrogen atom or the like, or is combined together with R 3 to form alkylene, X 1 is alkylene, and X 2 is a single bond or alkylene).
