Recently, peroxyacetyl nitrate (PAN) has been postulated to be a potential tropospheric reservoir of oxides of nitrogen, and to be important in their long-range transport. To better assess its atmospheric chemistry, absolute rate constants for the reaction of OH radicals with peroxyacetyl nitrate (PAN) have been determined using a flash photolysis resonance fluorescence technique. Rate constants of (1.13¿0.06)¿10-13 cm3 molecule-1 s-1 and (1.37¿0.05)¿10-13 cm3 molecule-1 s-1, independent of total pressure over the range 25-100 torr of argon, were determined at 273¿2 and 297¿2 K, respectively. (The errors limits represent two standard deviations; systematic errors could contribute an additional -10% uncertainty.) These rate constants imply that reaction with the OH radical is the most important removal process for PAN in the upper troposphere.