The Claus process is an efficient way of removing H2S from acid gas streams and it has been widely practised in industries such as natural gas processing, oil refining and metal smelting. Catalytic stage plays a paramount role in Claus units performance, Different samples of Claus reaction alumina catalyst were characterised by the fractal dimension parameter employing nitrogen adsorption porosimetry. The influence of such a dimension over Claus reactor performance was studied employing a reactor model. Significant differences between fractal and smooth catalysts performance were found as well as implications in reactor design. Deactivated catalyst samples were also characterised and its behaviour as Claus catalyst shows influence of the fractal dimension value. Fractal dimension appears as a useful parameter to the Claus catalyst selection procedure.