Ring-opening and dimerization reactions of methyloxirane and cis- and trans-2,3-dimethyloxirane were studied on CuZSM-5, prepared by various methods, and HZSM-5 zeolites in a closed static recirculation reactor at 363 K in reductive atmosphere. On these materials two main reaction types, ring-opening and dimerization, could be observed. For methyloxirane the major transformation pathways were ring opening and dimerization, producing various dioxolane and dioxane derivatives. In addition to these routes 2,3-dimethyloxiranes underwent deoxygenation and rearrangement as well. The activities and selectivities of the transformations toward these pathways were found to be significantly different depending on the stereochemistry of the substrates as well as the nature of the catalysts. Suggestions for the active sites and transformation mechanisms are also offered.