The influence of extracellular polymeric substances originated from benthic algae on particle aggregation and sedimentary stabilization in the Ariake Sea was investigated through laboratory experiment. Extracellar polymeric substances in the lyophilized sediment were isolated as a colloidal carbohydrate fraction. The influence of the polymeric substances on particle aggregation and sedimentary stabilization was experimentally examined through rheological measurement. The rheological properties of polymeric subustances solution and sediment slurry with polymeric subistances in the presence of calcium ions were evaluated using a shear rate changeable rehometer. The aqueous solution of polymeric substances solution behaved as Bingham fluids, and the shear stress increase with elapsed time, probably due to hydration. The sea sediment slurry with polymeric substances behaved as a non-Bingham fluid. The stress-strain hysteresis loop width predicts the interaction of sediment and polymeric substances. Polymeric substances enhance sediment stabilization, and the effect is greatly improve by calcium ions.