Abstract Electric conductivities have been studied for Langmuir molecular layers of barium salt of fatty acids and for the layers of barium arachidate mixed with all-trans-β-apo-8′-carotenoic acid. These results have been interpreted based on an electron tunneling model taking account of the mirror image force. The conduction levels of the layers have thereby been estimated to be 1.00 eV for barium stearate, 1.31 eV for barium arachidate and 1.45 eV for barium behenate below vacuum level. The conduction level of the carotenoic acid has been derived to be 1.9 eV from these results. The structure of these layers has been discussed from the above mentioned experimental results, together with those on surface pressure, absorption spectrum and electric capacitance.