A rate constant for the reaction of NO 3 with propene has been determined by an absolute rate technique at room temperature and atmospheric pressure. Experiments were performed in a Pyrex photoreactor coupled to two multiple reflection optical systems interfaced to a FTIR spectrometer and a UV-visible grating spectrometer. These two spectrometric devices allowed us a time-resolved monitoring of propene and NO 3 radicals. We propose the following rate constant: k propene+NO 3 = (6.4 ± l.l) × l0 −15 cm 3 molecule −1 s −1 . This value is in good agreement with three published values but is about 30% lower than three other determinations and than the value recommended by frequently used bibliographic evaluations. As propene has been widely used as a reference compound in many other kinetic studies, implications of this reevaluation are briefly discussed. C 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 73-81, 2009