The invention relates to a double-stranded ribonucleic acid (dsRNA) for inhibiting the expression of the Eg5 gene (Eg5 gene), comprising an antisense strand having a nucleotide sequence which is less that 30 nucleotides in length, generally 19-25 nucleotides in length, and which is substantially complementary to at least a part of the Eg5 gene. The invention also relates to a pharmaceutical composition comprising the dsRNA together with a pharmaceutically acceptable carrier; methods for treating diseases caused by Eg5 expression and the expression of the Eg5 gene using the pharmaceutical composition; and methods for inhibiting the expression of the Eg5 gene in a cell.