The stoichiometry and rate of the reaction of H2S (0.05-0.80% in N-2) with high surface area ZnO have been studied at 273-318 K. Absorption of H2S by ZnO is not accompanied by evolution of the stoichiometric amount of H2O which has a catalytic action via chemisorption as surface hydroxide. Shallow bed reactors have been used to limit the conversion, providing rate data at nearly uniform gas composition. Three reaction regimes have been identified being, in order of decreasing rate, gaseous diffusion-reaction of H2S, formation, desorption, and diffusion of H2O, and solid state diffusion. The fast rates appear to depend upon the crystallite size and morphology, as influenced by the thermal and environmental history of the sample and doping of the ZnO by divalent ions or Na+ The rate in the slowest regime is independent of H2S partial pressure and zinc oxide conversion and is promoted by water vapor. The mechanism appears to involve proton transfer from adsorbed H2S to chemisorbed OH.