The rate coefficient for the reaction O(P-3) with ClONO2, k(1), was measured between 202 and 325 K using two methods : pulsed laser photolysis with time-resolved atomic resonance fluorescence detection of the O atoms and pulsed laser photolysis with long-path tunable diode laser absorption for detection of NO3 radicals. The measured rate coefficient. is summarized by k(1) = (4.5 +/- 1.4) x 10(-12) exp[(-900 +/-80)/T]cm(3) molecule(-1) s(-1), with k(I)(298 K) = (2.2 +/-0.2) x 10(-13) cm(3) molecule(-1) s(-1). The yield of NO, radical in this reaction was measured to be essentially unity. Our results are compared with those from previous studies.