The reaction of C-60 With ozone in toluene results in the formation of C-60 oxides. C60O and two isomers of C60O2 were isolated; they both have the 423 nm absorption peak characteristic of an epoxide structure between adjacent 6,6-rings in C-60. Intact molecular ions are generated by electrospray ionization (ESI) without fragmentation. The enhanced ESI sensitivity of the higher oxides reflects the increase in electron affinity upon oxidation. In contrast to ESI, odd-numbered fragments are observed in laser desorption ionization (LDI) of C60O. The two isomers of C60O2 show different intensity distributions of the same fragment ions in LDI, suggesting different distances between the two oxygen atoms in them. Mechanisms are proposed for the formation of the two isomeric forms of C60O2 and for mass spectrometric fragmentation processes.