This work aims for the development and characterization of a new biosorbent with enhanced capacity for recovery of Cr(III) from aqueous solutions. The adsorbent was developed by chemical modification of pine bark (Pinus pinaster) (PB). Initially, several chemical agents (HCl, H2SO4, HNO3, H3PO4, citric acid, acetic acid, NaOH) were tested, but the best results were obtained with NaOH. The adsorbent developed was characterized regarding chemical composition and thermal behaviour before and after chemical modification. Scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS) showed the morphology and the most relevant elements on the surface before and after adsorption of Cr(III). Fourier transform infrared spectroscopy (FTIR) revealed the important role of carboxylate groups in Cr(III) uptake. The adsorption process was studied under different conditions, namely for testing the particle size (in the ranges from 0.088 to 0.149 and 0.250 to 0.595 mm). The equilibrium isotherms showed that Cr(III) adsorption is strongly dependent on particle size. According to the Langmuir model, the maximum adsorption capacity of Cr(III) increased from 17.15 to 31.40 mg/g as the particle range decreased. The experimental Cr(III) removal efficiencies as a function of the adsorbent dosage were well predicted by the mass balance equation for the batch adsorption process coupled with the equilibrium isotherm.