Biosorption of Cr(VI) ions from aqueous solutions and electroplating wastewater by walnut shell powder has been investigated in a batch biosorption process. The biosorption of Cr(VI) ions was found to be dependent pH, initial chromium ion concentrations, biosorbent dose, contact time and temperature. The experimental equilibrium biosorption data were analyzed by Langmuir, Freundlich, and Temkin isotherm models. The Langmuir model gave a better fit than the Freundlich and Temkin models. The maximum biosorption capacity calculated from the Langmuir isotherm was 138.89 mg/g at optimum conditions. The kinetic studies indicated that the biosorption process of the chromium ions followed well pseudo-second-order model. The negative values of Go (-3.51 kJ/mol) and positive value of Ho (12.95 kJ/mol) revealed that the biosorption process was spontaneous and endothermic. Biosorption process was successfully applied to the treatment of an electroplating wastewater sample, where the concentration of chromium (VI) ions, organic materials and COD were effectively reduced. According to the sorption capacity, walnut shell powder considered as an effective, low cost, and environmentally friendly biosorbent for the removal of Cr(VI) ions from aqueous solution and electroplating wastewater.