In present study, removal of nickel ions (Ni (II)) from synthetic wastewater using Fe3O4 nanoparticles modified by oak shell was investigated. The FTIR analysis of the adsorbent suggested the occurrence of interaction between the carboxyl group on oak shell modified magnetic nanoparticles (OSMMN) surface and Ni (II). Also, the morphology and size of the adsorbent were observed by SEM and TEM. Additionally, the effect of different parameters such as contact time, adsorbent dose, solution pH and initial concentration of nickel (II) ions were investigated on the adsorption of nickel. The adsorption experiments showed that the maximum Ni(II) adsorption was obtained as contact time = 15 min, temperature = 25 °C, adsorbent dosage = 2.6 g/L, and pH = 4.5. In these conditions, 93.88% Ni(II) was removed from aqueous solution. Moreover, in order to study equilibrium behavior of adsorption, Langmuir and Freundlich isotherm models were applied. The results showed that the experimental data were fitted well with the Langmuir isotherm model, and the maximum adsorption capacity of the adsorbent using Langmuir model was determined to be 454.54 mg/g which was a considerable amount.