The UV absorption spectrum and the photolysis reaction kinetics of 4-hydroxy-3-hexanone (4H3H) in the 275-330 nm region have been investigated for the first time. The photolysis frequency of this compound in the atmosphere was evaluated using actinometry and found to be J(4H3H,atm) = (5.9 +/- 3.1) x 10(-3) h(-1). An atmospheric effective quantum yield was estimated to about 10% and a photolysis lifetime of about 7 days was determined. The comparison with the reactivity of other hydroxyketones suggests that the kinetics of hydroxyketones photolysis depends on their structure, mainly the branching and the proximity of the two functions. (C) 2017 Elsevier B.V. All rights reserved.