Benzyltrimethylammonium hydroxide, also known as Triton B or trimethylbenzylammonium hydroxide, is a quaternary ammonium salt that functions as an organic base.

The compound is colourless, although the solutions often appear yellowish.

[1] Commercial samples often have a distinctive fish-like odour, presumably due to the presence of trimethylamine via hydrolysis.

Together with the benzyltriethylammonium salt, benzyltrimethylammonium hydroxide is a popular phase-transfer catalyst.

It is also used as a base in Ando's Z-selective variant of Horner-Wadsworth-Emmons Olefination reactions.