Dimethyl dithiophosphoric acid is the organophosphorus compound with the formula (CH<sub>3</sub>O)<sub>2</sub>PS<sub>2</sub>H. It is the processor for production of the organothiophosphate insecticide Malathion. Although samples can appear dark, the compound is a colorless, distillable liquid.
It is prepared by treating phosphorus pentasulfide with methanol: