The fluorescence spectra and the fluorescence decay following excitation by means of a light flash were studied for a few simple aliphatic ketones to obtain evidence for excimer formation. The fluorescence spectra of 2-pentanone recorded in iso-octane and in tert-butanol at a number of ketone concentrations show no sign of excimer luminescence. The monomer fluorescence decay kinetics were studied for 2-pentanone in two solvents over a wide range of ketone concentration and for acetone, methyl isopropyl ketone and diisopropyl ketone at one concentration. For all these ketones under all the conditions investigated only double-exponential functions gave a satisfactory fit to the experimental data. The observations were interpreted as evidence for singlet excimer formation in a reversible process. The lifetimes of the excited singlet monomer and excimer and the rate coefficients of the formation and removal of the excimer were determined for 2-pentanone in iso-octane and tert-butanol.