The rate constant for the reaction of OClO with NO at temperatures ranging from 220 to 367 K has been measured under pseudo-first-order conditions using the fast flow combined with a mass spectrometer (FF/MS) method. The rate constant for the OClO reaction with NO is found to be negatively dependent on temperature, with an Arrhenius expression of k(4) = (1.04 +/- 0.24) x 10(-13) exp[(347 +/- 58)/T] cm(3) molecule(-1) s(-1), which is in contrast to that estimated by NASA kinetic data review panel on the basis of a previous measurement at 298 K. The atmospheric implication of our experimental results is discussed. (C) 2002 Elsevier Science B.V. All rights reserved.