The present invention provides a lipid nano-particles, which allow nucleic acids to be easily introduced into cells, comprising a cationic lipid represented by formula (I) (wherein: R 1 and R 2 are, the same or different, alkenyl, etc, and X 3 is absent or is alkyl, etc, X 1 and X 2 are hydrogen atoms, or are combined together to form a single bond or alkylene, and Y 1 is absent or anion, L 1 is a single bond, etc, R 3 is alkyl, etc), and a cationic lipid represented by formula (II) (wherein: R 9 and R 5 are, the same or different, alkenyl, etc, and X 4 and X 5 are hydrogen atoms, or are combined together to form a single bond or alkylene, and X 6 is absent or is alkyl, etc, Y 2 is absent or anion, a and b are, the same or different, 0 to 3, and L 9 is a single bond, etc, R 6 is alkyl, etc, L 2 and L 3 are -O-, -CO-O- or -O-CO-), and the like.
