MgO doped with Nd 2 O 3 has been evaluated as a catalyst for the oxidative coupling of methane (OCM) reaction. It is demonstrated that significant improvements in methane conversion efficiency and selectivity to C 2 products (as compared to pure MgO) can be achieved. The level of catalytic improvement is shown to be dependent on the Nd 2 O 3 concentration and the precise catalyst preparation method. Detailed transmission electron microscopy studies have been performed on the Nd 2 O 3 /MgO catalysts prepared by an impregnation route and by a number of coprecipitation methods. Six distinct neodymia morphologies on the MgO support have been identified. These are (i) crystalline thin films, (ii) Nd 2 O 3 crystallites attached to the MgO support, (iii) isolated Nd 2 O 3 needles, (iv) epitaxial microclusters, (v) disordered thin films, and (vi) isolated clusters. The relative proportions of these Nd 2 O 3 morphologies in the catalysts are also shown to depend upon the neodymia loading and the preparation route. Cross-correlation between microstructural observations and catalytic performance data for these materials enable us to deduce that the disordered neodymia films, which probably contain some dissolved Mg 2+ ions, are largely responsible for the improvement in OCM performance.