The inhibitive action of aqueous extract of Cassia acutifolia (CA) plant on Al-Cu alloy corrosion in 2M HCl, H3PO4 and H2SO4 solutions was studied using weight loss, potentiodynamic and impedance measurements. The inhibition was found to increase with increasing concentration of CA extract. The adsorption behaviour of CA extract followed Flory – Huggins and thermodynamic – Kinetic isotherms. The effect of temperature range (25-65oC) on the corrosion behaviour of Al-Cu alloy in 2M HCl solution indicated that the inhibition efficiency of CA extract decreases with rise of the temperature leading to physical adsorption. Thermodynamic parameters are calculated from Arrhenius transition state equation. Polarization curves showed that CA extract acts as cathodic type inhibitor. Tafel slopes are more or less constant suggesting that the action of CA extract does not affect the mechanism of corrosion process. The results obtained show that the CA extract could serve as an effective inhibitor for the corrosion of Al-Cu alloy in HCl solution.