Xylulose is a ketopentose, a monosaccharide containing five carbon atoms, and including a ketone functional group. It has the chemical formula . In nature, it occurs in both the <small>L</small>- and <small>D</small>-enantiomers. 1-Deoxyxylulose is a precursor to terpenes via the DOXP pathway.
<small>L</small>-Xylulose accumulates in the urine in patients with pentosuria, due to a deficiency in L-xylulose reductase. Since <small>L</small>-xylulose is a reducing sugar like <small>D</small>-glucose, pentosuria patients have been wrongly diagnosed in the past to be diabetic.