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A series of cobalt catalysts supported on mixed magnesium-lanthanum oxide (Co/Mg-La) was synthesized using various methods of introducing the active phase precursor on the support, i.e. deposition-precipitation (DP), deposition-precipitation using urea (DPU) and wet impregnation method (WI). The activity measurements in ammonia synthesis reaction revealed significant differences in the performance of catalysts obtained by these methods. Particularly high activity, several times higher than the activity for other catalysts, was observed for the WI catalyst. The detailed physicochemical characteristics (N₂ physisorption, XRPD, TPR, H₂-TPD, SEM-EDX, CO₂-TPD, FTIR-DRIFT, XPS) enabled the identification of chemical state of the catalysts surface. The factors determining outstanding catalytic performance of WI catalytic system were indicated as low level of hydrogen poisoning and favorable basicity of the surface.