Abstract. The electrochemical behaviour of two water soluble redox species (pentacyano(L)ferrate(II) complexes, where L is 4,4'-bipyridine and ammonia), belonging to cyanoferrate(II) series, was investigated by using cyclic voltammetry (CV) technique in a "middle phase microemulsion" (MPME). The microemulsion (ME) is formed between water and toluene, by using, besides the redox species, sodium dodecyl sulphate as surfactant, 1-butanol as cosurfactant and sodium chloride as supporting electrolyte. Three different three-electrode configuration arrangements were used. In each case reversible behaviour for both species was obtained. Different behaviour was found in "middle phase" for the two investigated electroactive species based on the presence of the sixth ligand (coligand). The coligand determines, on one hand, different electronic influence on the electron transfer reaction at Pt working electrode and, on the other hand, specific interaction with the "microscopic organic phase" from "middle phase". This paper demonstrates, based on Randles-Sevcik equation, that [Fe(CN) 5 (4,4'-bpy)] 3-is distributed between the "water phase" and "microscopic aqueous phase" rather in latter phase. For [Fe(CN) 5 (NH 3 )] 3-, its distribution is similar with that of the common hexacyanoferrate(III) or hexacyanoferrate(II). The CV study of the two different electroactive species illustrates an almost reversible behaviour both in "middle phase" and "water phase". (doi: 10.5562/cca1999)