The present invention provides a cationic lipid, which allow nucleic acids to be easily introduced into cells, represented by formula (I)(wherein: R1 and R2 are, the same or different, alkenyl, etc, and X1 and X2 are hydrogen atoms, or are combined together to form a single bond or alkylene, andX3 is absent or is alkyl, etc,Y is absent or anion,a and b are, the same or different, 0 to 3, andL3 is a single bond, etc,R3 is alkyl, etc,L1 and L2 are -O-, -CO-O- or -O-CO-),a composition comprising the cationic lipid and a nucleic acid, anda method for introducing a nucleic acid into a cell by using the composition comprising the cationic lipid and the nucleic acid, and the like.
