Two major enzymes, monooxygenase and dioxygenase, were exampled and explained to understand the microbial degradation mechanisms of BTEX (benzene, toluene, ethylbenzene, and xylene). And we investigated and reported the related microbial species of each enzyme. In addition, we reviewed the degradation mechanism and pathway of each substrate. Lastly, we added the microbial degradation properties under the various conditions.