Nitrous oxide is an important component in the Earth's atmosphere with a global budget that shows significant imbalance between known sources and sinks. A recent isotopic analysis of atmospheric nitrous oxide has suggested that back fluxing from the stratosphere could be an important source of N2O to the troposphere. To quantitatively determine the potential magnitude of this process, the relevant isotopic fractionations must be known. We have measured the isotopic fractionation factors associated with the two known stratospheric sink reactions of N2O: photolysis and photooxidation. It is observed that nitrous oxide photolysis produces no fractionation in Δ18O and Δ17O, while photooxidation produces a small mass-dependent enrichment in 18O and 17O in the residual N2O. ¿ American Geophysical Union 1995