Eukaryotic DNA ligases play vital roles in DNA replication, recombination and repair through catalyzing ligation of nick in double-stranded DNA with an ATP-dependent reaction. DNA ligase Ⅲ(Lig3) is a unique ligase which is located in both nucleus and mitochondrion. Lig3 plays important roles in base excision repair and other single-stranded break repairs with its DNA repair protein XRCC1. But Lig3 is more important in maintenance of mitochondrial DNA (mtDNA) integrity without XRCC1-dependent DNA repair. These researches provide new perspective for Lig3 function and DNA repair.