Abstract: This paper represents the results of an investigation on phytoplankton and water quality in Xiangxi River Watershed during the period from October 1996 to July 1997 and 2003.The results showed that the composition of phytoplankton was dominated by the species of diatoms,green algae and blue-green algae.Diatoms were the most important component,followed by green algae and blue green algae in the period of 1996-1997.In 2003,green algae sat at the primary position,and diatoms were the second.Other algae had also varied in different degree.The cell densities of phytoplankton were changed seasonally.The maximum value and the minimum value were noted in summer and winter,respectively.The water quality of Xiangxi River Watershed had a little destroyed during 6 years.The trophic status of the watershed is at α-β-mesotrophy level,nowadays.