The present study focuses on the valorization of an agricultural waste, olive cores that have been chemically activated by an oxidizing agent (H3PO4) in order to improve its adsorptive capacities. For a better orientation of its uses a range of physicochemical tests has been carried out: the ash content (1.87 %), the moisture content (1.089 %), the iodine value (317.26 mg·g-1) and the isoelectric point (pHPZC = 3.2). In order to test the performance of our activated carbon, we chose the Bemacid Blue (BB) dye as a pollutant. The adsorption of this dye was monitored by UV-Visible spectrophotometer. Several parameters have been studied, including contact time, temperature, initial concentration, adsorbent dosage. The kinetics and thermodynamics of adsorption of Bemacid Blue by activated olive cores were studied. The adsorption kinetics have been well described by the pseudo second order model. The adsorption kinetics seem to satisfy the Langmuir isotherm model (R2 = 0.9931) with respect to the Freundlich and Temkin isotherms. This study demonstrated that chemically activated olive cores can be used as a new adsorbent for the treatment of water contaminated by textile dyes.