Three novel diquaternary ammonium salts with alkanediyl spacers of varying chain length were synthesized, and their corrosion inhibition effects on N80 steel in 15 wt % HCl solution were studied by weight loss measurement, electrochemical polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDX). The results indicated that the inhibition efficiency increased with the inhibitor concentration and the length of hydrophobic spacer of the inhibitor. At 90 degrees C, the inhibition efficiency of diquaternary ammonium salt N,N'-octane-1,8-diyl-bisquinolinium dibromide reached about 91% at the inhibitor concentration of 0.01 mol/L. Potentiodynamic polarization curves indicated that all synthesized compounds acted as mixed-type inhibitors. The inhibition mechanism involved the formation of an inhibitor protective layer on the N80 steel surface by a Langmuir-type adsorption process. The presence of Br and N in chemical composition detected by EDX confirmed the adsorption of inhibitors on the N80 steel surface.