Chemically modified natural saw dust (CMSD) was prepared via hydrothermal reaction between citric acid and sawdust then the CMSD characterized using some qualified techniques such as scanning electron microscopy (SEM) and FT-IR. The adsorption capability of modified sawdust towards Hg(II) was significantly increased because of the introduction of carboxylic groups on CMSD' surface during the modification, and the adsorption capability was linearly reliant on carboxylic sites level to some extent. The prepared CMSD was employed for uptake of Hg2+ from different samples. Sorption parameters; which include pH, temperature, sorption's time and sorption's concentration were evaluated to determine the best conditions for sorption. In addition, the sorption uptake of CMSD was 80 mg g-1. The samples including Hg2+ was used as analytical applications on the present method and the observed-data is promising.