Fenthion is an organic thiophosphate that is O,O-dimethyl hydrogen phosphorothioate in which the hydrogen atom of the hydroxy group is replaced by a 3-methyl-4-(methylsulfanyl)phenyl group. It exhibits acaricidal and insecticidal activities. It has a role as an EC 3.1.1.7 (acetylcholinesterase) inhibitor, an acaricide, an agrochemical, an avicide, an EC 3.1.1.8 (cholinesterase) inhibitor and an insecticide. It is functionally related to a 4-(methylsulfanyl)-m-cresol.