The catalytic efficiency of the chloro[5,10,15,20-(1,3-dimethylimidazolium-2-yl)porphyrinatomanganese(III)] tetraiodide is evaluated in the epoxidation of olefins under homogeneous conditions, using hydrogen peroxide as oxidant. The catalytic behaviour of this metalloporphyrin is strongly dependent on the co-catalyst used; high conversions are found for all olefins studied, affording the corresponding epoxides as the major products.