The kinetics of the reaction of SO radicals with NO2 have been studied in a discharge flow reactor combined with an electron impact ionization quadrupole mass spectrometer at nearly 2 Torr total pressure of helium and in the temperature range 220–960 K. The reaction rate constant was determined under pseudo-first order conditions in excess of NO2 over SO using two different methods for generation of the SO radicals: k1 = (6.7 ± 0.2) × 10−12 exp(295 ± 10)/T) cm3 molecule−1 s−1 (the uncertainties represent precision at the 2σ level, the estimated total uncertainty on the rate constant being 15% at all temperatures). The present measurements indicate that the current recommendations for k1 underestimate the rate constant at low stratospheric temperatures and overestimate it at the high temperatures characteristic of combustion.