The results of kinetic measurements using the innovative nanostructured cyclically refreshable liquid amalgam film silver–based electrode (R-AgLAFE) indicated the accelerating influence of 2-thiocytosine and water activity in the multistep of Bi(III) electroreduction in chlorate(VII) related to the ‘cap-pair’ effect. The highest catalytic activity was observed for 1 mol·dm−3 chlorate(VII) solution. The nature of the rate constants changes in the function of potential points out to the existence of a multistage process of Bi(III) ion electroreduction in the presence of 2-thiocytosine as well as insignificant changes in the Bi(III) electroreduction mechanism in the presence of 2-thiocytosine in solutions with small water activity as compared to those with large water activity. In this mechanism, the chemical stages of Bi–(RS–Hg) active complexes formation (located inside the adsorbate layer) with the participation of 2-thiocytosine, which is a mediator in their formation, can be distinguished. Probably, their different structures and properties determine different catalytic activities. Keywords: Electroreduction; R-AgLAFE; ‘Cap-pair’; 2-Thiocytosine; Active complexes