The presence of heavy metals such as cadmium in water resources is becoming a severe environmental and public health problem. Many removal techniques have been used such as adsorption, chemical precipitation, ion exchange, and reverse osmosis to remove of heavy metals pollutant. Adsorption method is one of the common methods because it is simple, low-cost, effective and flexible in design and operation. Nowadays nanoscale adsorbents specially magnetic nanoparticles as iron oxide nanoparticles (Fe 3 O 4 ) which magnetically separable are used for wastewater treatment. Functional group present on the surface of these nanoparticles is one of the important factors which determines adsorption capacity. By use of capability of immobilization of protein on this nanoparticles, we can immobilise heavy metal chelating protein as metallothionein, on this nanoparticle and adsorption capacity improve will be expected. The aim of this study was to immobilisation of OsMTI-Ib metallothionein isoform on silica-coated iron oxide (Fe3O4@SiO 2 ) nanoparticles and investigation of effect of this protein on cadmium (CdCl 2 .H 2 O) adsorption capacity of nanoparticles. OsMTI-Ib isoform was heterologously expressed in Escherichia coli strain Rosetta (DE3). The activity of protein for sorption of cadmium was confirmed by DTNB test and measurement of cadmium content in protein using atomic absorption spectroscopy (AAS). Nanoparticles were amino-functionalized using (EDS), then used to immobilization of protein. Nanoparticles surface were activated by glutaraldehyde. The protein was immobilized by covalent attachment and protein loading capacity (w/w %) on nanoparticles was calculated 40± 1.5 %. Nanoparticles containing protein and nanoparticles without protein were incubated for two hours with cadmium and amount of remaining cadmium was measured. Adsorption capacities of these nanoparticles were calculated. Comparison of adsorbed cadmium on nanoparticles containing protein and nanoparticles without protein showed that the nanoparticles containing protein due to have more amount of cadmium adsorption site have more adsorption capacity. In the nanoparticles without protein, cadmium ion was adsorbed by the coordination between cadmium ion and amino groups. In nanoparticles containing protein, thiol groups of protein adsorbed cadmium via mercaptid bound. The Effect of time on the amount of sorption indicated that the adsorption capacity in both of nanoparticles increased with increasing of time. Investigation of kinetic models of adsorption process has shown that in the both of adsorbent, adsorption process controlled by pseudo-second-order kinetic model. Investigation of the effect of initial concentration of cadmium on adsorption capacity showed that the adsorption capacity increased with increasing of initial concentration. Investigation of adsorption isotherm models has shown that the experimental data were fitted to the Langmuir model. According to this model the maximum adsorption capacities for nanoparticles containing protein and nanoparticles without protein were 477.88 mg/g and 315.8 mg/g respectively. Investigation of the effect of pH showed that in the both of nanoparticles, adsorption capacity decreased with decreasing of pH. The decreasing of adsorption capacity attributed to the high concentration of H + . By increasing of concentration of H + , more amino and thiol groups protonated and competition between H + and Cd 2+ for attaching to surface of sorbent increased. Investigation of recovery and reusability of nanoparticles containing protein and nanoparticles without protein showed that these nanoparticles retained more than 70% of their initial activities after 3 and 4 times’ reuse respectively. The decreasing of activity was probably due to the change in protein structure, separation of silica cover or lose of nanoparticles in recovery process. Results of this study showed that the immobilization of OsMTI-Ib isoform on Fe3O4@SiO 2 nanoparticles improved the cadmium adsorption capacity in these nanoparticles. Key words : Iron oxide nanoparticles, Immobilization of protein, Metallothionein, Pseudo-second-order kinetic model, Langmuir model