The rate of sulfur transfer across the gas/solid interface involving H2S(g) and Fe1-x surface has been investigated using resistance relaxation measurements at 600 degrees C. The rate of the oxidation reaction incorporating sulfur into Fe1-x has been found to decrease with sulfur activity (a(S)) in the sample as (a(S))(-2/3), while the rate of the reduction reaction corresponding to sulfur loss is found to increase with the sulfur activity as (as)(1/3). The kinetic finding has been combined with the appropriate defect models for FeS to identify the rate limiting step for the sulfur transfer reaction from H2S to FeS. Accordingly, the rate limiting step has been identified to be : H2S(g) + 2e(-) = S2-(ad) + H-2(g).