Trimethyl borate is the organoboron compound with the formula B(OCH<sub>3</sub>)<sub>3</sub>. It is a colourless liquid that burns with a green flame. It is an intermediate in the preparation of sodium borohydride and is a popular reagent in organic chemistry. It is a weak Lewis acid (AN = 23, Gutmann-Beckett method).
thumb|This chemical is quite flammable and burns with a green flame
Borate esters are prepared by heating boric acid or related boron oxides with alcohols under conditions where water is removed by azeotropic distillation.
: ArMgBr + B(OCH<sub>3</sub>)<sub>3</sub> → MgBrOCH<sub>3</sub> + ArB(OCH<sub>3</sub>)<sub>2</sub>
:ArB(OCH<sub>3</sub>)<sub>2</sub> + 2 H<sub>2</sub>O → ArB(OH)<sub>2</sub> + 2 HOCH<sub>3</sub>