The invention relates to iRNA, e.g., double stranded ribonucleic acid (dsRNA), compositions targeting the complement factor C3 gene, and methods of using such iRNA, e.g., dsRNA, compositions to inhibit expression of a C3 gene and to treat subjects having a complement component C3-associated disease, e.g., paroxysmal nocturnal hemoglobinuria (PNH), atypical hemolytic uremic syndrome (aHUS), atypical hemolytic uremic syndrome (aHUS), neuromyelitis optica (NMO), multifocal motor neuropathy (MMN), myasthenia gravis (MG), and C3 glomerulonephritis.