Total dissolved organic carbon (TOC) in waters is always one of important factors to assess water quality. In this paper, we propose a simple procedure based on carbon measurements by ANATOC II analyzer to estimate the total dissolved organic carbon in waters of the river system in Hanoi. Our results which were carried out during the year of 2003 showed that carbon contents in the dissolved faction in this river system existed mainly in the organic form and that TOC contents strongly influenced the vegetation and climate.
