The influence of Al₂O₃ nanoparticles on corrosion inhibition of benzotriazole (BTA) in brass/ simulated water system was studied by potentiodynamic polarization curve and electrochemical impedance spectroscopy (EIS). The results show that BTA has good corrosion inhibition effect on brass. Al₂O₃ nanoparticles could reduce the corrosion inhibition performance of BTA. The higher the concentration of Al₂O₃ nanoparticles in simulated water, the lower corrosion inhibition performance of BTA. The isothermal adsorption of BTA on brass surface in simulated water and Al₂O₃ nanofluids was analyzed. The results indicated that the adsorption of BTA on brass surface followed the Langmuirs’ adsorption isotherm, the adsorption Gibbs free energy ΔG was less than −40 kJ/mol, corresponding to chemical adsorption, in both simulated water and Al₂O₃ nanofluids. The −ΔG value of BTA on brass surface decreased in Al₂O₃ nanofluids, indicating the weakening of the BTA adsorption on the brass surface. Surface analysis of brass samples by optical microscope and X-ray diffraction confirmed the above results.