Threose is a four-carbon monosaccharide with molecular formula C4H8O4.

It has a terminal aldehyde group, rather than a ketone, in its linear chain and so is considered part of the aldose family of monosaccharides.

The threose name can be used to refer to both the d- and l-stereoisomers and more generally to the racemic mixture (d/L-, equal parts D- and L-) as well as to the more generic threose structure (absolute stereochemistry unspecified).

The prefix "threo-" which derives from threose (and "erythro-" from a corresponding diastereomer erythrose) offer a useful way to describe general organic structures with adjacent chiral centers, where "the prefixes... designate the relative configuration of the centers".

[3] As is depicted in a Fischer projection of d-threose, the adjacent substituents will have a syn orientation in the isomer referred to as "threo", and are anti in the isomer referred to as "erythro".