The rate coefficient of the reaction of HSO with O3 at five temperatures in the range 273-423 K was determined by means of the discharge-flow/laser-induced-fluorescence technique. The laser-induced fluorescence of HSO was detected by the gated photon-counting technique; a detection limit approximately 4 X 10(9) molecules cm -3 was achieved. The reaction was carried out under pseudo-first-order conditions with [03] much greater than [HSO]; the rate coefficient was determined to be k = (4.7 +/- 1.0) X 10(-14) CM3 Molecule-1 s-1 at 298 K, approximately 30% greater than, but within experimental uncertainty of the only previous measurement by Wang and Howard by means of the discharge-flow/laser-magnetic-resonance technique. The temperature dependence of the rate coefficient is expressed in the Arrhenius form, k(T) = (2.1 +/- 0.7) X 10(-12) exp[- (1120 +/- 320)/T] cm3 molecule-1 s-1.