Dimethylphosphine is the organophosphorus compound with the formula (CH3)2PH, often written Me2PH.

It is a malodorous gas that condenses to a colorless liquid just below room temperature.

Although it can be produced by methylation of phosphine, a more practical synthesis involves the reduction of tetramethyldiphosphine disulfide with tributylphosphine:[1] The compound exhibits the properties characteristic of a secondary phosphine, i.e., a compound of the type R2PH.

It can be oxidized to the phosphinic acid: It can be protonated to give the dimethylphosphonium ion: With strong bases (e.g., lithium amide, it can be deprotonated to give dimethyl phosphide derivatives (e.g., lithium dimethyl phosphide):