The hydroxymethyl group is a substituent with the structural formula −CH2−OH.

It consists of a methylene bridge (−CH2− unit) bonded to a hydroxyl group (−OH).

This makes the hydroxymethyl group an alcohol.

It has the identical chemical formula with the methoxy group (−O−CH3) that differs only in the attachment site and orientation to the rest of the molecule.

[1][2] Hydroxymethyl is the side chain of encoded amino acid serine.