Mercury thrown even at a low concentrations in water resources causes a severe threat to ecosystem hence the presented work describes a low cost and environmentally friendly clean up platform for decontamination of water in terms of mercury ions. For this purpose MgFe2O4 – Gum Arabic composite was prepared with a simple ultrasound assisted precipitation route and further modified with L-cysteine as a thiol resource to improve its adsorption characteristic. The structure of biosorbent was characterized with XRD, FESEM, VSM, EDX, and BET techniques. Effective parameters on mercury adsorption were optimized with response surface methodology (RSM) using Box-Behnken design (BBD). Maximum removal efficiency was obtained at pH of 5, contact time of 15 min and adsorbent dosage of 19 mg by magnetic GA. After thiol functionalization optimum variables changed to pH of 2, time of 15 min and dosage of 5 mg. Isotherm study indicated that mercury biosorption onto the magnetic Gum Arabic and thiol immobilized sorbent followed Langmuir and Freundlich model with adsorption capacity of 96 and 250 mg g-1, respectively. Results for kinetic study revealed that mercury adsorption followed pseudo – second order model. To study the ability of biosorbent as a reusable compound a mixture of HCl (0.5 mol L-1) and thiourea (2%) was employed to release the adsorbed ions from the sorbent surface moreover, it showed 90% removal efficiency after three cycles of sorption and desorption which confirmed the presented composite is a reusable biosorbent.