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 R1 is alkenyl or the like, R2 is alkenyl or the like, R3 and R9 are each alkyl, or are combined together to form alkylene, or R3 and R5 are combined together to form alkylene, R5 is a hydrogen atom or the like, or is combined together with R3 to form alkylene, X1 is alkylene, and X2 is a single bond or alkylene).
