The quantum yields for the production of NO3 in the gas-phase UV photolysis of peroxyacetyl nitrate (PAN, CH3C(O)OONO2) and peroxypropionyl nitrate (PPN, CH3CH2C(O)OONO2) at 248 and 308 nm were measured. We report room-temperature quantum yield values of 0.19 +/- 0.04 and 0.41 +/- 0.10 at 248 and 308 nm, respectively, for PAN and 0.22 +/- 0.04 and 0.39 +/- 0.04 at 248 and 308 nm, respectively, for PPN. UV absorption cross sections for PPN between 200 and 340 nm over the temperature range 296-253 K are also reported. The atmospheric implications of these results are discussed.