Two biodegradable, non toxic cationic gemini surfactants having ester linkage in the spacer namely, CmH2m+1(CH3)(2)N+(CH2COOCH2)(2)N+(CH3)(2)CmH(2m+1.)2C1(-) (m-E2-m, m = 12, 14), were synthesized and characterized using elemental analysis, FF-IR and H-1-NMR. The corrosion inhibition performance of synthesized compounds separately and in combination with sodium salicylate (SS), along with the nature and stability of inhibitive film, for mild steel (MS) in 1 M HC1 solution at 30-60 degrees C was evaluated using weight loss, potentiodynamic polarization, EIS, UV-visible spectroscopy, FTIR, SEM/EDAX, TGA and quantum chemical calculations. Results of the studies confirm m-E2 -m as effective corrosion inhibitor for MS in HCI; the inhibition effect being synergistically strengthened in presence of SS. The synthesized compounds act as mixed type inhibitor and adsorb on MS surface in accordance with Langmuir adsorption isotherm. Experimentally measured inhibition efficiencies are correlated with the molecular parameters obtained using PM6 semi-empirical method. Empirical results are in good agreement with the theoretical predictions. (C) 2017 Elsevier B.V. All rights reserved.