Dimethylphosphite is an organophosphorus compound with the formula (CH3O)2P(O)H, known as dimethyl hydrogen phosphite (DMHP).

Dimethylphosphite, is a minor tautomer of the phosphorus(V) derivative.

It is a reagent for generating other organophosphorus compounds, exploiting the high reactivity of the P-H bond.

The compounds can be prepared by methanolysis of phosphorus trichloride or by heating diethylphosphite in methanol.

[1] Although studies have not been reported for this compound, the closely related diethylphosphite exists predominantly as the phosphorus(V) tautomer.