Disclosed is a cationic lipid which is represented by formula (I) and makes it easier to introduce a nucleic acid into a cell. (In formula (I), R<1> and R<2> may be the same or different and each represents an alkenyl group or the like; X<1> and X<2> each represents a hydrogen atom, or alternatively X<1> and X<2> combine together to form a single bond or an alkylene group; X<3> is absent or represents an alkyl group or the like; Y is absent or represents an anion; a and b may be the same or different and each represents a number of 0-3; L<3> represents a single bond or the like; R<3> represents an alkyl group or the like; and L<1> and L<2> each represents -O-, -CO-O- or -O-CO-.) Also disclosed are: a composition that contains the cationic lipid and a nucleic acid; and a method for introducing a nucleic acid into a cell, using the composition that contains the cationic lipid and a nucleic acid.