The oxygen isotopic fractionation, which occurs during ozone decomposition, has been determined, complementing earlier studies on the fractionation during ozone formation. Oxygen produced in the decomposition is depleted in heavy isotopes in a mass-independent fashion. The mechanism for the mass-independent effect is unknown, though the fractionation magnitude information is required for modeling the steady-state isotopic composition of stratospheric ozone. ¿ American Geophysical Union 1988