The present invention relates to iRNA such as double stranded RNAs (dsRNA), the composition of targeting complement component C5 genes and the methods for inhibiting using such iRNA (such as dsRNA), composition the expression of C5 and treating the subject with a kind of associated diseases of complement component C5 (for example, paraoxysmal nocturnal hemoglobinuria).本發明涉及iRNA例如雙鏈核糖核酸(dsRNA)、靶向補體組分C5基因的組合物以及使用此種iRNA(例如dsRNA)、組合物來抑制C5的表達並且治療患有一種補體組分C5相關聯的疾病(例如,陣發性睡眠性血紅蛋白尿症)的受試者的方法。