Abstract: Effect of light irradiation on the accumulation of phenolic compounds was investigated in the flesh slices of three apple (Malus domestica Borkh.) cultivars. 'Fuji' and 'Jonathan' with red skin and 'Orin' a yellow-green one were used in this study. The irradiation was carried out at 10, 17, 24 and 30C for 96 hours, using a mixture of white plus ultraviolet fluorescents. Phenolic acids, anthocyanin and flavonols were the phenolics that increased rapidly by irradiation whereas flavanols, procyanidins and dihydrochalcones did not change in either mature or in ripe fruits of all the three cultivars. There was a positive correlation between anthocyanins, phenolic acids and flavonols in examined cultivars both at the mature and ripe stages. Optimum temperature for the synthesis of phenolic acids, anthocyanins and flavonols was 24C regardless to the maturity stage and variety. Total phenolic content of 'Fuji' increased through ripening but it decreased in 'Jonathan' and 'Orin'. Therefore, the irradiation to the flesh might be a very useful method for the study of the regulation mechanism of the phenolic compounds accumulation.