Abstract: Nitrate is one of the major sources of pollution in water bodies. To reveal how the excessive nitrate accumulation affects the release of VOCs and causes the odor in the water, we analyzed the cell growth and VOCs from Microcystis aeruginosa and M. flosaquae--the primary species responsible for the cyanobacterial bloom--under the NaNO3 stress. Compared to the control NaNO3 significantly reduced the cell growth of M. aeruginosa and M. flos-aquae by 29.6% and 43.0% respectively after the 24h stress. Under the normal condition, M. aeruginosa and M. flosaquae released 26 and 27 compounds respectively, and the major types of VOCs were sulphide, hydrocarbons, terpenoids, benzenes, aldehydes and esters. In M. aeruginosa the release of these 6 VOCs was remarkably increased by 60.5%, 14.3%, 136.6%, 92.1%, 730.0% and 120.7% respectively after the NaNO3 treatment, and the increments in M. flos-aquae were 172.7%, 162.5%, 154.0%, 55.9%, 51.2% and 109.4% respectively. In addition, 4 new compounds were found in VOCs of M. aeruginosa under the NaNO3 stress, and 1 new compound was found in VOCs of M. flosaquae. Therefore, the stress of excessive nitrate accumulation on algae may promote the release of VOCs, which could aggravate the odor and the quality of the water.