DNA ligases are important enzymes of DNA metabolism. The reaction of nicked DNA joining catcalyzed by the DNA ligase is required in DNA replication and in DNA repair pathways that require the re-synthesis of DNA.The recent advances in isozyme DNA ligase are summarized: bacteria DNA ligases are all NAD^＋-dependent and their sequences show a considerale degree of similarity and all are approximately the same size (～75 ku). All known eukaryotic DNA ligases are powered by ATP. DNA ligase Ⅰ is required for Okazaki frament joining and some repair pathways; DNA ligase Ⅱ appears to be a degradation product of ligase Ⅲ; DNA ligase Ⅲ has several isoforms, which are involved in repair and recombination of DNA.