In this study, spent coffee grounds (SCG) were treated using sodium hypochlorite (NaClO) to remove organics. The NaClO-treated SCG was modified with 3-aminopropyltriethoxysilane (APTES) to improve its adsorption performance. To understand the characteristics of the prepared adsorbents, samples were characterized by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The pH edge, kinetic, and isotherm experiments were conducted to evaluate the adsorption performance of APTES-SCG for Reactive Black 5 (RB5), Reactive Orange 16 (RO16), and Reactive Yellow 2 (RY2). The pH edge experiments were carried out in the pH range of 2-12 at an initial dye concentration of 100 mg/L. The results showed that the dye uptakes on APTES-SCG increased with decreasing pH value. The adsorption experiments for kinetics confirmed that the equilibrium time was reached within 30 min at pH 2. The adsorption isotherm experiments were performed at initial dye concentrations of 30 to 300 mg/L, and the experimental data were well-fitted by the Langmuir model. The dye-loaded APTES-SCG was desorbed using 0.01 M NaOH solution and repeated adsorption-desorption experiments showed that APTES-SCG could be reused at least 3 times.