A discharge-flow modulated molecular beam mass spectrometry technique has been used to determine the rate constant for the reaction of ground state oxygen atoms with C2H4S in the temperature range 220–950 K. The reaction rate constant has been determined directly by monitoring C2H4S in an excess of O atoms and through competitive reaction of oxygen atoms with C2H4S and Br2. Weak, negative temperature dependence is observed below 300 K, whereas positive temperature dependence is observed above 380 K: k = 1.13 × 10–12 (T/298)2.18 exp(733/T) cm3 molecule–1 s–1. We estimate this expression to be accurate within 15% over the investigated temperature range. SO and C2H4 have been detected as reaction products and a branching ratio of unity (with uncertainty of 10%) has been found for the channel forming these two species in the temperature range 300–900 K, confirming that the title reaction is an efficient source of SO radicals.