The present invention provides a lipid nano-particles, which allow nucleic acids to be easily introduced into cells, comprisinga cationic lipid represented by formula (I)(wherein: R1 and R2 are, the same or different, alkenyl, etc, and X3 is absent or is alkyl, etc,X1 and X2 are hydrogen atoms, or are combined together to form a single bond or alkylene, andY1 is absent or anion,L1 is a single bond, etc,R3 is alkyl, etc), anda cationic lipid represented by formula (II)(wherein: R9 and R5 are, the same or different, alkenyl, etc, andX4 and X5 are hydrogen atoms, or are combined together to form a single bond or alkylene, andX6 is absent or is alkyl, etc,Y2 is absent or anion,a and b are, the same or different, 0 to 3, andL9 is a single bond, etc,R6 is alkyl, etc,L2 and L3 are -O-, -CO-O- or -O-CO-), and the like.
