With low price and its superior adsorption performance after modification, currently agricultural waste is used as adsorbent of heavy metals in wastewater, which has become a hot research topic. To study on Hg2+ from wastewater absorbed by lemon residues that has been modified by 15% concentration of sulphuric acid. The pore volume, pore size and other properties of the adsorbent were test. The samples were characterized by differential thermal analysis, IR, electron microscopy and spectroscopy. The result showed that the adsorption rate was controlled by membrane diffusion kinetics that was viewed as the first order kinetics equation of the Lagergren, which was physically absorbed. The adsorption properties of modified lemon residues were improved greatly, and the pore size distribution mainly was medium. There were three losses-weight process. There was a endothermic peak around 66 degrees C and two exotherm near 316 degrees C and 494 degrees C. Basic framework of Lemon residues was not changed and structure of Lemon residues was amorphous; the surface of modified lemon residues loosen and many pores formed, and Hg2+ have been adsorbed effectively.