Motivated by Yung and Miller's [1997> suggestion that N2O is isotopically fractionated during UV photolysis in the stratosphere, we have studied the photolysis rates of the 14N15N16O and 15N14N16O structural isotopomers. In this study, we follow the concentrations of these compounds with FTIR spectroscopy during photolysis at 213 nm. When fitted to a Rayleigh fractionation model, the observations yield single-stage enrichment factors of &egr;(14N15N16O/14N14N16O)=-73¿5 per mil and &egr;(15N14N16O/14N14N16O)=-41¿10 per mil. As predicted by Yung and Miller [1997>, the photolysis rate of 15N14N16O is faster than 14N15N16O at this wavelength. The magnitude of the observed fractionation, however, is significantly larger than predicted. ¿ 2000 American Geophysical Union