Cephalosporin acylases (CA) are enzymes that catalyze hydrolysis of the acyl side chain of cephalosporin C(CPC) or glutaryl 7-cephalosporanic acid(GL-7ACA) to yield 7-aminocephalosporanic acid(7-ACA), the most important compound in the production of many semisynthetic cephalosporin antibiotics. According to their substrates, cephalosporin acylases can be classified into two classes: CPC acylase and GL-7ACA acylase. CA was divided into five types on the basis of their homologies and mass of molecules, and the structures of their genes; some properties of these enzymes were discussed. Comparison of N-terminal nucleophile hydrolases and CA shows that CA may belong to N-terminal nucleophile hydrolases family. Thus it makes easy to understand further their physiological roles.