Two kinds of dissolved organica matter (DOMc and DOMr) prepared from Ruditapes philippinarum and Phragmites communis, which are the common species in aquatic ecosystems, were used to study the characteristic of mercury (Hg) adsorption onto sediment collected from Jiaozhou bay. The results exhibited that Langmuir equation and Freundlich equation both better fitted to the Hg isothermal adsorption process onto sediment in all treatments. The addition of the two kinds of DOM had the obvious stimulative action to Hg adsorption onto sediment compared with that in the control groups. Moreover, DOMc had a slightly higher promotion action at Hg adsorption to sediment than that by DOMr. Compared with the control groups, the maximum of adsorption in two samples were elevated by 116% and 117% in DOMc treatment, and 110% and 109% in DOMr treatment, respectively. And then, the organic matter and pH were the important factors influencing Hg adsorption ability to sediment. In general, the organism in aquatic ecosystem could increase Hg adsorption quantity into sediment by the action of their DOM, with the result of the decrease of biological effectiveness of Hg. And this increased the amount of Hg in sediment to a certain extent, which increased the Hg risk in the water body.