Two benzothiazole derivatives, namely 2-(n-hexylamino)-4-(3′-N,N-dimethylamino-propyl)amino-6-(benzothiazol-2-yl)thio-1,3,5-s-triazine (BTC6T) and 2-(n-octylamino)-4-(3′-N,N-dimethylamino-propyl)amino-6-(benzothiazol-2-yl)thio-1,3,5-s-triazine (BTC8T), were synthesized to study their corrosion inhibiting effect against steel in a 1 M HCl solution. The corrosion inhibition efficiency was measured using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, and weight loss methods. Both inhibitors offered extra stability and higher inhibition efficiencies again steel corrosion than previously reported benzothiazole family inhibitors. These inhibitors can be adsorbed onto surfaces by both physical and chemical means. Finally, quantum chemical parameters were calculated using the density functional theory method (DFT) and the correlation between the theoretical and experimental results are discussed.