The retinal pigment epithelium (RPE) cells protect retina from oxidative stress. The deterioraton of its protective function may lead to the etiology of age-related macular degeneration. It is known that the amounts of RPE melanosomes decline with age. However, the molecular mechanisim of this phenomenon and the structural changes of the modified melanin remain little known. Melanocytes produce two types of pigment, eumelanin and pheomelanin. Eumelanin consists of 5,6-dihydroxyindole (DHI) and 5,6‐dihydroxyindole‐2‐carboxylic acid (DHICA), while pheomelanin consists of benzothiazine and benzothiazole units. Melanins can be analyzed through specific degradation products by HPLC. Alkaline hydrogen peroxide oxidation (AHPO) of eumelanin gives pyrrole-2,3,5-tricarboxylic acid (PTCA) and thiazole-2,4,5-tricarboxylic acid (TTCA) as specific degradation products of DHICA moiety of eumelanin and benzothiazole moiety of pheomelanin, respectively. AHPO of synthetic and natural melanins show that the photoaging of eumelanin gives rise to pyrrole-2,3,4,5-tetracarboxylic acid (PTeCA, produced by cross-linking), leading to the increase in the ratio of PTeCA/PTCA. Benzothiazine pheomelanin can be analyzed by reductive hydrolysis, as 4-amino-3-hydroxyphenylalanine (4-AHP) and 3‐amino‐4‐hydroxyphenylalanine (3‐AHP). In this study, we compared changes in various melanin markers and their ratios in human melanocytes exposed to UVA, in isolated bovine RPE melanosomes exposed to strong blue light and in human RPE cells from donors of various ages. The results indicate that the PTeCA/PTCA ratio is a sensitive marker for the photo-oxidation of eumelanin and that both eumelanin and pheomelanin in human RPE cells undergo extensive structure modifications/degradations due to the life-long exposure to blue light. The decreased amounts of eumelanin could lead to deterioration of its ability to protect RPE cells against oxidative stress. Further, because of the generation of a more complex, sterically crowded 3D structure, the degraded eumelanin might have a lowered potential to sequester toxic iron and to scavenge reactive oxygen species.