Modification of magnetite (Fe3O4) nanoparticles with activated carbon of Pulai leaveshas been carried out. Magnetite (Fe3O4) nanoparticles were synthesized from natural sand of Padang beach West Sumatra and activated carbon was extracted from Pulai leaves. Structural and morphological properties of magnetite nanoparticles were studied using X-Ray Diffractometer (XRD) and Scanning Electron Microscope (SEM) respectively. Elemental composition of the samples was identified using X-Ray Fluorescence Spectroscopy (XRF). The heavy metal (cooper) adsorption was determined using Ultra Violet Visible light Spectroscopy (UV-Vis). The ability of magnetite(Fe3O4) nanoparticles modified with activated carbon for adsorbing the cooper ion in Siak river water is discussed.The results indicate that magnetite (Fe3O4) nanoparticlesmodified with activated carbon of Pulai leavescan absorb heavy metal Cu contained in Siak river water.