Six new monoadducts of C(70) with oxygen species have been prepared, isolated, and characterized following ozonation of C(70) solutions. The initial products are two ozonide monoadducts, identified as a,b- and c,c-C(70)O(3). These ozonides lose O(2) through thermolysis or photolysis to form various isomers of C(70)O. The a,b-C(70)O(3) isomer dissociates through thermolysis with a decay time of 14 min at 296 K to form the [6,6]-closed epoxide a,b-C(70)O. When photolyzed, it instead forms a [5,6]-open oxidoannulene identified as a,a-C(70)O. These reactions mimic those seen for C(60)O(3). By contrast, the c,c-C(70)O(3) isomer, which has a thermolysis lifetime of 650 min at 296 K, decays thermally only to an oxidoannulene deduced to be d,d-C(70)O. Photolysis of c,c-C(70)O(3) produces a mixture of the oxidoannulenes b,c-C(70)O and c,d-C(70)O plus a minor amount of the c,c-epoxide. All four C(70)O oxidoannulene isomers undergo photoisomerization, giving eventually the a,b- and c,c-C(70)O epoxides.