18O16O is the sixth most abundant gas in the atmosphere after 14N14N, 16O16O, Ar, 15N14N and H2O. From available data on line positions in the Schumann-Runge (S-R) bands (175<&lgr;<205 nm) of 18O16O we estimate its atmospheric photodissociation rates. In the high stratosphere and mesosphere this proposed source of O and O3 could be significant compared to photodissociation of 16O16O although our estimates are subject to several uncertainties that are discussed. We calculate the transmission of solar radiation through the S-R bands of 18O16O and 16O16O with transmission functions averaged over individual S-R bands. Line-by-line calculations will be needed to refine our estimates but certain spectroscopic data are not yet availbale.