The products obtained from limonene epoxidation can be used as intermediates or precursors in organic and pharmaceutical synthesis. Commercial magnesium oxide was evaluated as a heterogeneous catalyst in the epoxidation of R-(+)-limonene using H₂O₂ in a Payne reaction system, using acetonitrile as an oxidant activator and water and acetone as solvents. The effect of temperature and the concentration of catalyst, H₂O_2, and limonene were evaluated; the highest yields for limonene epoxide (80%) and diepoxide (96%) were found at 50 °C and 30 min and 2 h, respectively. Fresh and spent catalysts were characterized by X-ray diffraction, thermogravimetric analysis, N₂ adsorption–desorption isotherms, Fourier transform-infrared, and scanning electron microscopy-energy dispersive X-ray. The efficiency of H₂O₂ in the epoxidation reaction varied between 100 and 20% in the time range of 0–30 min for all tested reaction conditions. The production of peroxyacetimidic acid as an intermediate oxidant in the limonene epoxide synthesis was described using a pseudohomogeneous reversible model (E = 58.61 kJ mol^–1), while the heterogeneous model describes both the decomposition of H₂O₂ (E = 29.06 kJ mol^–1) and the epoxidation of limonene with the intermediate (E = 52.28 kJ mol^–1). Leaching tests verified the heterogeneity of MgO which was used in four consecutive cycles.