The present invention provides a composition for suppressing the expression of a KRAS gene, comprising a lipid particle containing, as a drug, a double-stranded nucleic acid having an antisense strand having a sequence of bases complementary to the sequence of at least 19 continuous bases of any one KRAS genes mRNA of sequence Nos. 1 to 3 anda cationic lipid represented by the following formula (I):whereinR1 and R2, which are the same or different, are each linear or branched alkyl, alkenyl or alkynyl having a carbon number of from 12 to 24 L1 and L2, which are the same or different, are each —CO—O— or —O—CO— a and b, which are the same or different, are each 1 to 3 and R3 is a hydrogen atom, alkyl having a carbon number of from 1 to 6, or alkenyl having a carbon number of from 3 to 6, and the like.
