AbstractThis study examined the efficacy of Inula Racemosa leaves in the adsorption of Brilliant Cresyl Blue (BCB) from aqueous solutions. The study uses both experimental and theoretical research, including Density Functional Theory (DFT), to gain a better understanding of how the adsorbent and Brilliant Cresyl Blue molecules interact with each other. We determined the point zero value of the charged powder of Inula Racemosa and characterized the functional groups using FTIR spectroscopy. The experimental results indicate a significant ability of our adsorbent to adsorb the cationic dye Brilliant Cresyl Blue, and we have identified optimal conditions for its effective removal. The results suggest that the most effective amount of our biosorbent was 0.1 g. The equilibrium period for biosorption was 10 min, and the biosorbent capacity for biosorption improved with increasing pH. The Pseudo‐second‐order model accurately predicts the retention of Brilliant Cresyl Blue using Inula Racemosa. The Freundlich model was found to be better suitable for analyzing the isotherm data, revealing a maximum adsorption capacity of 3.49 mg g−1, achieving an efficiency removal of 89.95 %. We compared Density Functional Theory (DFT) calculations with experimental observations to validate the theoretical predictions and improve our understanding of the adsorption mechanism. Docking simulations show how the molecules of Inula Racemosa and Brilliant Cresyl Blue interact with each other, including the interactions of hydrogen bonds and electrostatic forces.