Corrosion inhibition of mild steel in 1N HCl solutions was investigated in the absence and presence of different concentrations of some mercapto-quinoline derivatives namely, 3-((phenylimino)methyl)quinoline-2-thiol (PMQ) and 3-((5-methylthiazol-2-ylimino)methyl)quinoline-2-thiol (MMQT) by using conventional weight loss, potentiodynamic polarization, linear polarization, electrochemical impedance spectroscopy, and scanning electron microscopic studies. By EIS and weight loss measurements, it was found that PMQ and MMQT were effective inhibitors and their inhibition efficiency was significantly increased with increasing concentrations of inhibitors. Polarization curves showed that the evaluated PMQ and MMQT both act as mixed inhibitions. The adsorptions of these inhibitors on the mild steel were found to follow the Langmuir adsorption isotherm. Results show that the rate of corrosion of mild steel increased with increasing temperature over the range 25 degrees-45 degrees C both in the presence of inhibitors and in their absence. Activation energies in the presence and absence of PMQ and MMQT were obtained.