Activated carbon (AC) was synthesized from Phoenix dactylifera stones and then modified by CoFe2O4 magnetic nanocomposite for use as a Cr(VI) adsorbent. Both AC/CoFe2O4 composite and AC were fully characterized by FTIR, SEM, XRD, TEM, TGA, and VSM techniques. Based on the surface analyses, the addition of CoFe2O4 nanoparticles had a significant effect on the thermal stability and crystalline structure of AC. Factors affecting chromium removal efficiency like pH, dosage, contact time, temperature, and initial Cr(VI) concentration were investigated. The best pH was found 2 and 3 for Cr adsorption by AC and AC/CoFe2O4 composite, respectively. The presence of ion sulfate had a greater effect on the chromium sorption efficiency than nitrate and chlorine ions. The results illustrated that both adsorbents can be used up to seven times to adsorb chromium. The adsorption process was examined by three isothermal models, and Freundlich was chosen as the best one. The experimental data were well fitted by pseudo-second-order kinetic model. The half-life (t1/2) of hexavalent chromium using AC and AC/CoFe2O4 magnetic composite was obtained as 5.18 min and 1.52 min, respectively. Cr(VI) adsorption by AC and AC/CoFe2O4 magnetic composite was spontaneous and exothermic. In general, our study showed that the composition of CoFe2O4 magnetic nanoparticles with AC can increase the adsorption capacity of AC from 36mg/L to 70mg/L.