Biacetyl is a molecule that is well characterized in the gas phase, on silver and quartz surfaces, and in matrix isolated studies, but its photochemistry has not been documented on alkali halide films. The focus of this research was to determine the photochemistry of biacetyl on alkali halide films, estimate the upper limits of the kinetics of biacetyl relaxation and reaction, and calculate the quantum efficiencies from the irradiation of biacetyl and its photoproducts at various excitation wavelengths of UV light. Biacetyl was adsorbed onto films of NaCl, NaBr, KCl, and KBr at low temperatures and pressures, then photolyzed throughout the UV spectrum at temperatures of 13 K, 50 K, and 100 K. The photoproduct isolated was CO at 2130 cm-1. Two questionable photoproducts arising at 1718 cm-1and 1831 cm-1 were assumed to be the acetyl radical and acetone, but there is some evidence contradicting that assumption. The rate constants for the relaxation of excited biacetyl returning to the ground state were examined, and are consistent with literature values.1 The quantum efficiencies were calculated using known coefficients and were found to be higher than expected due to either a lack of output photons from the light source or migration of biacetyl on the salt films. Compared with studies done in the gas phase, matrix isolation studies, and silver/quartz surface studies, biacetyl does not undergo the extent of photochemistry expected due to salt surface quenching.