The isomerization and metathesis of cyclopropane were carried out over a series of reduced molybdena-alumina catalysts (1.7-13 wt% Mo). The distribution of Mo oxidation states was determined by XPS, The average Mo oxidation state estimated from XPS agreed with that obtained by measuring the O-2 consumption on reoxidation for a given catalyst. A good correlation was found between the catalytic activity for the isomerization reaction and the relative intensity of the XPS peak attributed to paired double-bonded Mo (TV) species (as in MoO2), The results indicate a direct relationship between these Mo (IV) species and the coordinative unsaturated sites involved in the formation of metallocyclobutane. The latter is reportedly the intermediate required for the isomerization reaction to take place.