This research presented a method to synthesize magnetic nanocrystalline cellulose-based nanocomposites using in-situ co-precipitation technique to produce ferromagnetic oxide particles (Fe3O4) that were grafted on the surface of cellulose nanocrystals (CNCs). The synthesized material was used to remove lead ions from aqueous solutions. Different physicochemical analyst techniques such as XRD, FTIR, SEM, and TEM were used to characterize the structure of the material upon the different ratios of cellulose nanocrystals/ Fe3O4. The XRD analysis showed that CNC/Fe3O4 nanocomposite has characteristic diffraction peaks corresponding to Fe3O4 and cellulose nanocrystals. The FTIR spectrum indicated the specific functional groups of Fe3O4 and CNC in the nanocomposite materials. The size of nanoparticles produced in this work were less than 15 nm with Fe3O4 and roughly 25 nm with CNC via image SEM and TEM. According to these studies, with the same Pb2+ concentration in water of 200 ppm, the best condition for homogenous materials was the 1:1 ratio (cellulose nanocrystals: Fe3O4) and the absorption capacity at time balance (qe) was 0.1132 mg/g. The lead adsorption of material was evaluated by the ICP-OES measurement method. The equilibrium data fitted the Freundlich isotherm model better than the Langmuir isotherm model. The new adsorbent can help removing 60 % of Pb2+ from the solution and can be magnetically separated from the continuous phase.