Abstract: The photodegradation of dissolved organic carbon (DOC) and chromophoric dissolved organic matter (CDOM) was investigated in surface Pearl River estuary water in summer 2015 and winter 2016. The results revealed both DOC and CDOM decreased exponentially with irradiation time. The contents of photochemical labile DOC and CDOM were higher in the freshwater endmember, induced by the influence of terrigenous- and sewage-derived organic matter, and the fraction decreased seaward. The relative content of photochemical labile DOC was up to 50% in winter in the freshwater endmember, which was significantly higher than that in summer, whereas no obvious seasonal variation for CDOM. This demonstrated more transparent dissolved organic matter (DOM) participated indirect photochemistry in winter. Under natural conditions, the photodegradation rates of DOC and CDOM in summer were about 4 times and 2.5 times of those in winter, respectively, due mainly to the differences of temperature and solar irradiance. Our results also suggested photochemistry should be an important sink of DOM during its transport from the Pearl River to the shelf. Moreover, the aromaticity and molecular weight of DOM decreased rapidly during irradiation and then kept relatively constant, which suggested aromatic DOM with higher molecular weight was the dominant substrate of photodegradation.