In order to elucidate photofading mechanism of aerated alcoholic solution of model cyan dye with carbonyl compound (CCPD), 1) effect of acid on photofading of alcoholic solution of model cyan dye with CCPD, 2) effect of NaOH on photofading, 3) effect of oxygen concentration, 4) absorption change of the photolytically faded solution by keeping in dark, addition of NaOH-EtOH solution and light irradiation after unsealing, are examined at various conditions. Also photofading product in aerated alcoholic solution of model cyan dye with CCPD is examined by mass spectroscopy. It is confirmed that photofading of the solution is initiated by ketyl radical of CCPD and following reactions resulted in formation of mono-oxygenated dye or degradation of the dye are probably started from monohydrogenated dye radical.