Corrosion inhibition of Al-Cu alloy in 1.5 M NaOH by extract of Cassia acutifolia (CA) plant was studied using chemical and electrochemical measurements. The inhibition efficiency was found to increase with increasing concentration of CA extract. The adsorption behaviour followed Flory – Huggins and thermodynamic – Kinetic isotherms. The effects of temperature range (25-65oC) on the corrosion behaviour indicate that the inhibition efficiency of extract decreases with rise of temperature leads to physical adsorption. Thermodynamic parameters were calculated from Arrheinius transition state equation. Polarization curves showed that extract act as cathodic inhibitor. Tafel slopes are more or less constant indicating that the action of extract has no effect on the mechanism of corrosion process. The results obtained show that the CA extract could serve as an effective inhibitor of the corrosion of Al-Cu alloy in NaOH solution.