The purpose of this work was to study the catalytic effect of activated carbon particles 7.5 μm in diameter on the initial oxidation rate of bisulphide, with oxygen as oxidant, in an aqueous solution buffered at a pH of 9.7 and at temperatures of 48.5, 35 and 25 °C. Two reactors were used: a stirred gas—liquid contactor to determine the kinetics and a continuous flow reactor to demonstrate that a continuous process is possible. The liquid phase oxidation of sulphide was found to be much faster in the presence of activated carbon. Kinetic equations for the initial rate of reaction are given separately for homogeneous and heterogeneous oxidation. As activated carbon shows a strong catalytic activity, it can be of interest in the oxidation of sulphide in industrial and other waste waters at low temperatures.