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The kinetics for the sulphidation of a Ni-20 wt. % Cr alloy at 0-9700 C and sulphur potentials below 10 atmospheres have been studied using a thermogravimetric technique. The morphology of the reaction product was studied using optical microscopy, electron probe micro analysis and X-ray techniques. The kinetics were observed to be parabolic at sulphur potentials below 5 x 10-lO atmospheres with rates much slower than those reported for pure chromium under similar conditions. The parabolic kinetic reaction rate consta~t was found to vary as a semilogarithmic function of sulphur potential. The reaction product consisted of an external scale, identified as mainly Cr s,3 4 with dissolved nickel up to 5 % and a subscale with morphological break-down of the alloy/external sc;ale interface. Approximate determinations of the diffusivity of chromium in the alloy and the scale as well as sulphur diffusivity in the alloy have been made. Tentative m ·echanisms have been proposed to explain the diffusion control of the reaction and the stabilization of the external scale by dis solved nickel. I {iii