The present invention provides a kind of compositions, KRAS genes for inhibition of gene expression, contain including lipid particle, as drug, it is 1 to 3 that double-strandednucleic acid, which has the sequence nucleotide sequence number of any one KRAS gene mRNA of at least 19 continuous bases of the base sequence of sequence complementation with antisense strand, And cation lipid expression (I): same or different in whereinR1 and R2, it is 12 to 24 that respectively linear or branch alkyl, alkenyl or alkynyl, which have carbon number, It is same or different in L1 and L2, respective-CO-O- or-O-CO- A and B, which be it is same or different, respectively 1 to 3 AndR3 is hydrogen atom, and it is 3 to 6, etc. that there is alkyl 1 to 6 carbon or alkenyl, which to have carbon number,.
