1,3-Cyclopentanedione is an organic compound with the formula (CH<sub>2</sub>)<sub>3</sub>(CO)<sub>2</sub>. It is one of two isomeric cyclopentanediones, the other being 1,2-cyclopentanedione. The enol is predicted to be about 1-3 kcal/mol more stable than the diketo form. The enol structure has been confirmed by X-ray crystallography.
The compound is prepared by hydrogenation of 2-cyclopentene-1,4-dione using zinc/acetic acid.