A poly(glycidyl methacrylate) (PGMA) grafted bentonite (Bent) was prepared by surface-initiated atom transfer radical polymerization (SI-ATRP), followed by modification with tetraethylenepentamine (TEPA) through a ring-opening reaction of the epoxy groups in PGMA to form polyamine grafted bentonite (Bent–PGMA–TEPA). The as-prepared novel material was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermal gravimetric analysis (TGA). The ability of Bent–PGMA–TEPA to adsorb Orange I (OI), a negatively charged dye, was tested. The effects of pH, initial concentration, contact time and temperature were investigated. The equilibrium adsorption isotherm and adsorption kinetics fitted well with the Langmuir model and the pseudo-second-order kinetic model respectively.