Hydrolysis of Ethyl-Cyanophos (Organophosphorus Compounds) Has Been Studied In Acidic Medium With Catalysts Such As Zr4+, Ce4+, Hf4+ and Th4+ Cations and the Rate Maxima Observed Were at Around Ph 2.0. Since the Metal Aquo Complexes Are Known to Exist In Equilibrium With Deprotonated Species and Therefore, Metal Bound Oh- Nucleophile Might Be Available Abundantly Even In Acidic Aqueous Solutions. Thus an Interaction of Sulphur of P=S Group With Metal Cation Followed By an Intramolecular Nucleophilic Attack of Hydroxy Anion at the Ester Phosphorus Atom Would Results In Cleavage of P-O Bond.