Objective: In this paper, we have introduced topoisomerase inhibitors, mechanism of action and types of them. DNA topoisomerases are ubiquitous enzymes that catalyze essential enzymes to solve the topological problems accompanying key nuclear processes such as DNA replication, transcription, repair and chromatin assembly by introducing temporary single or double strand breaks in the DNA. Results: There are two types of DNA topoisomerase: I and II, which are enzymes that control the changes in DNA structure by catalyzing the breaking and rejoining of the phosphodiester backbone of DNA strands during the normal cell cycle. Topoisomerases are crucial for the several DNA functions (e.g. replication and transcription) that require the DNA to be unravelled, a process that generates tension and entanglement in DNA. Topoisomerase I breaks a single DNA strand while topoisomerase II breaks both strands and requires ATP for full activity. In both cases, the enzyme is covalently attached to the DNA through tyrosine residues in the active site.