Mixed Langmuir-Blodgett (LB) films of arachidic acid (AA) and [Ru(L)(totpy)(OH2)](ClO4)(2) (L = Ph2AsCH2CH2AsPh2; 4-totpy = 4'-(4-tolyl-2,2':6',2"-terpyridine)) complex (2:1) were used in the preparation of modified electrodes. The incorporation of the metallic complex into mixed monolayers is noticed from the surface pressure (pi -A) and surface potential (DeltaV-A) isotherms. The pi -A curves show a phase transition region between the expanded and condensed liquid states (LE-LC) at 35 mN/m, which is not present in the pin-A curves for pure AA monolayers. In the DeltaV-A isotherms there is a large expansion of the critical area and the difference between the minimum and maximum surface potential (Delta DeltaV) increases with the concentration of the ruthenium complex in the mixed monolayer. Combining the pi -A curve data with the ultraviolet-visible spectra for the corresponding LB films, the dissociation degree of the fatty acid within the mixed LB films is calculated as 0.67. The FTIR spectra confirm the partial dissociation of the acid. The cyclic voltammograms of the modified electrodes of AA/ruthenium complex (2:1) at pH = 8.1, in the presence of benzyl alcohol showed pronounced enhancement of the anodic current corresponding to the Ru-IV/Ru-III couple. This is indicative of an electrocatalytic behavior.