The electrochemical behavior of various 1-methyl-1′-alkylviologens (C1CnV2+: n=1, 7, 8, 9, 10, 12, 14, 16 and 18) was studied using an electrochemical quartz crystal microbalance (EQCM). Three different types of the frequency change-potential (Δf–E) curves were observed depending on the length of alkyl substituent during the cyclic voltammetry (CV) of the first redox step: for n=1 and 7, Δf was less than 30 Hz (reversible); for n=9, 10, 12 and 14, Δf=200 Hz indicating electrodeposition of C1CnV+; for n=16 and 18, Δf=5000 Hz with two anodic peaks implying reorientation of the electrodeposited C1CnV+ occurring on the electrode surface. These results are consistent with our previous report where apparent dimerization of C1CnV+ was observed. The effect of cyclodextrins (CDs) on the frequency change-potential (Δf–E) curves was also investigated. Δf for 1 mM C1C16V2+ solution was 6000 Hz, while Δf was below 100 Hz in the presence of 13 mM of α-CD. However, Δf was 5000 Hz in the presence of 13 mM of β-CD. This implies that the complexation ability between C1C16V+/C1C16V2+ and α-CD is larger than that of β-CD through the tighter binding as per the report by Diaz et al. (J. Phys. Chem., 92 (1988) 3537). Comproportionation between C1C7V2+ and C1C7V0 in the presence of α- and β-CD was also carried out. A negligible effect was observed in the CV or Δf–E curve by α-CD. With β-CD, the anodic stripping wave (C1C7V0−e−→C1C7V+) disappeared, however, Δf was 9500 Hz (1100 Hz without CDs). It is clear that the complexation ability between C1C7V0 and β-CD is larger than that of α-CD. This might be due to the limited solubility of β-CD upon complexation with C1C7V0. A similar result was obtained in a 1 mM C1C4V2+ with 30 mM γ-CD experiment. The mechanism of the cyclodextrin-induced comproportionation reaction as well as electrodeposition pathways are discussed in this paper based on EQCM and spectroelectrochemical experimental results.