The aqai palm stalk (Euterpe oleracea) is a food residue used in its natural form (AS) and also protonated (AAS) as biosorbents for the removal of the textile dyes C.I. Reactive Black 5 and C.I. Reactive Orange 16 from aqueous solutions. This biosorbent was characterized by infrared spectroscopy, scanning electron microscopy, and nitrogen adsorption/desorption curves. The effects of pH, biosorbent dosage, and shaking time on the biosorption capacities were studied. In the acidic pH region (pH 2.0), the biosorption of the dyes was favorable. The contact time to obtain the equilibrium at 298 K was fixed at (10 and 4) h for the AS and AAS biosorbents, respectively, using both dyes. The Avrami fractionary-order kinetic model provided the best fit to the experimental data compared with the pseudofirst-order and pseudosecond-order kinetic adsorption models. The equilibrium data were fitted to the Langmuir, Freundlich, and Sips isotherm models. For both dyes the equilibrium data were best fitted to the Sips isotherm model.