Dimethylphosphine oxide is an organophosphorus compound with the formula (CH3)2P(O)H. It is a colorless liquid that soluble in polar organic solvents.

It exists as the phosphine oxide, not the hydroxy tautomer.

The compound arises by the hydrolysis of chlorodimethylphosphine:[1] Methanol, but not ethanol, can also be used in place of water, the co-product being methyl chloride.

Since chlorodimethylphosphine is dangerous to handle, alternative routes to dimethylphosphine oxide have been developed.

A popular method starts with diethylphosphite, according to the following idealized equations:[2] Chlorination gives dimethylphosphoryl chloride.