Abstract: Growth and physio biochemistry responses of Vallinseria spiralis L.were studied comparatively at ambient(about 350μmol mol-1 )and elevated(about 1000μmol mol-1 )CO2 concentration.Young plants under elevated CO2 grew faster than their counterparts in ambient CO2 at early stage.But as this superiority did not persist throughout the experiment,finally plants at CO2 enriched environment accumulated just 11.6% more total biomass than those at control.The total biomass advantage of the V.spiralis under elevated CO2 was primarily due to its leaf weight increment superiority over the control at the end of the experiment.More turions formed under elevated CO2.Root/leaf ratio trended to decrease under both elevated and ambient CO2,but no significant difference was detected.Under elevated CO2 chlorophyll and soluble protein content decreased,While total soluble sugar content increased significantly.