Water samples were collected during February 2020 from the Northern Andaman Sea and the area near the Preparis Channel to characterize, in addition to hydrographic parameters, the distribution, sources and fluorescent composition of chromophoric dissolved organic matter (CDOM). The distribution of dissolved organic matter (DOM) in the study area was predominantly affected by monsoon, precipitation, and terrestrial input. A barrier layer formed above the thermocline resulting from the freshwater input from the Irrawaddy River and Salween River, had a consistent effect on concentration of DOM in surface waters. Based on fluorescence excitation emission matrix (EEM) and parallel factor (PARAFAC) analysis, four fluorescent components were identified in the study area, including three humic-like substances (C1, C2 and C4, with their maximal Ex/Em at ≤240/418 nm, 315/384 nm and 270(360)/442 nm, and represented as peak A, M and A+C respectively) and one protein-like component (C3, with maximal Ex/Em at 275/334 nm, represented as peak T). Low levels of humic-like components were confined in the upper water column, consistent with strong photodegradation within the euphotic zone. In addition, C3, the protein-like component, accumulated concurrently in the surface layer, indicating sources from autochthonous DOM or biological activities.