The invention relates to a double-stranded ribonucleic acid (dsRNA) for inhibiting the expression of the proprotein convertase subtilisin kexin 9 (PCSK9) gene, comprising an antisense strand having a nucleotide sequence which is less than 30 nucleotides in length, generally 19-25 nucleotides in length, and which is substantially complementary to at least a part of the PCSK9 gene. The invention also relates to a pharmaceutical composition comprising the dsRNA together with a pharmaceutically acceptable carrier; and methods for treating diseases caused by PCSK9 gene expression by using the pharmaceutical composition.