Untreated wastewater can have important effects on the environment and human. The aim of the work was to evaluate the effectiveness of modified barley straw to remove malachite green from industrial wastewater. Studied variables were pH, contact time, initial malachite green concentration, and adsorbent dosage. Box–Behnken design method was used for modeling the process of adsorption. The results of analysis of variance showed that there are the significance relative among process parameters. The high value of R2 (0.9753) indicated that there was a high correlation between the predicted and experimental values. Removal efficiency of malachite green increased by increasing of modified barley straw dosage, pH and contact time, and decreasing of color concentration. Remove the color was better in alkaline conditions and the best pH was equal to 9.5. The optimum contact time to remove was 120 min. The findings of this study showed that Box-Behnken model can efficiently optimize the malachite green adsorption onto modified barley straw from aqueous solutions.