Different approaches such as precipitation, combustion, and hydrothermal method are available to prepare Fe3O4 nanoparticles. Respect to other methods, precipitation, especially with one iron source and natural reducing agents is a more green, economic, fast, and simple route for Fe3O4 synthesis. Based on these viewpoints, we have prepared Fe3O4 magnetic nanoparticles via a sonochemistry precipitation method using only one iron source and sugar, which was employed as a reducing agent. The combination of these prepared magnetic nanoparticles with polyphenylenediamine via an emulsion polymerization resulted in a magnetic polymer nanocomposite. The prepared magnetic material was characterized by Fourier transform infrared (FT-IR), scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and vibration sample magnetometer techniques. The magnetic nanocomposite was then successfully employed as an adsorbent in the removal of Pb2+ ions and Direct red 81 (DR-81) from single and binary solution. The results demonstrated that the maximum adsorption was obtained within 5min at pH 4.0 and also the adsorption processes of Pb2+ and DR-81 both were well fitted by pseudo-second-order kinetic model. The experimental data were analyzed by the Langmuir and Freundlich adsorption models. Freundlich model provided the best correlation of the experimental data for dye but lead adsorption well fitted with Langmuir model. Moreover, the maximum capacity of polymer nanocomposite was found to be 144.92 and 370.37mgg(-1) for DR-81 and Pb2+, respectively.