The aim of this study is to investigate the inhibit ion efficiency of N 1 ,N 1 ,N 5 ,N 5 -tetrakis((3,5-dimethyl-1H-pyrazol-1- yl)methyl)naphthalene-1,5-diamine (BF5), for mild s teel corrosion in 1.0 M HCl solution. For this purp ose, weight loss, electrochemical impedance spectroscopy and po tentiodynamic measurements were realized. The effec t of BF5 on the mild steel corrosion was also studied by qua ntum chemical calculations. Increasing inhibitor co ncentration led to significant reduction in the corrosion rate of mild steel, with inhibitor efficiency value abov e 97%. The corrosion behavior of steel in 1.0 M HCl without an d with the inhibitor at various concentrations was studied at the temperature range of 308 - 343 K. Potentiodynamic p olarization showed that this inhibitor as mixed-typ e inhibitor. The Nyquist plots showed that increasing BF5 concen tration, charge-transfer resistance increased and d ouble-layer capacitance decreased, involving increased inhibiti on efficiency. The adsorption of BF5 on the mild st eel surface was well described by the Langmuir adsorption model .