Background and purpose: Mercury is a toxic heavy metal which causes irrevocable intense nerve-recognition disturbance to human. Excess contact to mercury causes diseases like tremor, losing sensation, decreasing vision and hearing or growth. WHO recommended the most amount of mercury absorption about 0.3 mg per week and the most concentration in water about 1µg/L. The purpose of this study was to investigate the efficiency of Lcysteinefunctionalized single-walled carbon nanotubes (SWCNs) in mercury removal from aqueous solutions. Materials and methods: In this study, single-walled carbon nanotubes was used as absorbent. The effects of some parameters such as pH, absorbent dose, contact time and mercury concentration were assessed. All experiments have been done according to standard methods. The sample size was determined by Box-Benkan method. Results: The result showed that absorption rate increased by increasing of pH, contact time and mass CNTs dose. The Hg removal efficiency decreased by increasing of initial Hg concentration.The maximum and the minimum of absorption rate are 95 and 22 percent, respectively. ANOVA showed that RSM has a significant relationship for single-walled carbon nanotubes with linear conditions. Conclusion: The study demonstrated that SWCNT-Cysteine is a well absorbent for Hg removal from aqueous solutions Therefore, it can be effective for the removal of mercury from aqueous solutions.