The reaction of NO3 with C2H5I was studied using time-resolved cavity ring-down spectroscopy. The rate constant of NO3 + C2H5I reaction was determined to be (2.4 +/- 0.4) x 10 (13) cm(3) molecule (1) s (1) at 298 K and showed no pressure dependence in the range of 25-100 Torr of N-2 diluent. The determined value of the rate constant suggests that the reaction of NO3 with C2H5I would play an important role in the iodine cycle at night. (C) 2012 Elsevier B. V. All rights reserved.