Carboxylesterase belongs to the class of serine hydrolases family which includes Chymotrypsin and Acetylcholinesterase. Carboxylesterase is involved in the chemical reaction, exerting its role in catalyzing the carboxylic ester and water to convert to an alcohol and a carboxylate. Carboxylesterase is a type of enzyme that capable of hydrolyzing a variety of carboxylic acid esters and it's widely distributed in cells especially in mammalian liver. Carboxylesterase 5 (CES5), also known as cauxin or CES7, is one of CES enzyme families exerting role in catalyzing hydrolytic and transesterfication reactions with broad substrat specifity. CES5 is reported in high concentrations in the urine of adult male cats, and within a protein complex of mammalian male epididymal fluids. Roles for carboxylesterase 5 may include regulating urinary levels of cat pheromone, catalyzing lipid transfer reactions within mammalian male reproductive fluids, and protecting neural tissue from drugs and xenobiotics.