A convenient access to carbamoylmethylphosphine oxides (CMPO) in up to 96% isolated yield is developed via direct amidation of diphenylphosphoryl acetic acid in an ionic liquid as a recyclable reaction medium in the presence of triphenyl phosphite. The influence of the nature of the amine and anion and cation structure in the ionic liquid on the reaction rate and yields of the products are also investigated. 1-Butyl-3-methylimidazolium bromide [bmim]Br and trihexyltetradecylphosphonium chloride [P(C6H13)3(C14H29)]Cl proved to be the best media for carrying out this reaction.