Inclusion behavior of negatively charged host molecules, thiacalix[4]arene-p-tetrasulfonate (TC4AS) and [6]arene-p-hexasulfonate (TC6AS), toward (ferrocenylmethyl)trimethylammonium (FcCH 2 NMe3+), hydroxymethylferrocene (FcCH 2 OH), ferrocenecarboxylic acid (FcCOOH), and 1,1′-ferrocenedicarboxylic acid (Fc(COOH) 2 ) was studied in aqueous solutions (pH 7.0) with cyclic voltammetry. Upon increasing the concentration of TC4AS to 4-fold of each guest, the anodic peak current density (j p,a ) decreased, suggesting inclusion of the ferrocenyl guests in TC4AS. Also oxidation half-wave potential (E 1/2 ) of FcCH 2 NMe3+, FcCH 2 OH, and FcCOOH was shifted to cathodic direction, showing preferential inclusion of the oxidative state. Inclusion of neutral guests such as FcCH 2 OH and Fc + COO − implies that hydrophobic interaction between TC4AS and the guests is the chief driving force for formation of host–guest assembly. The decrease of E 1/2 for each guest was in the order: FcCH 2 NMe3+>FcCH 2 OH>FcCOOH, suggesting that electrostatic interaction controls the preference toward oxidative form of the guest. Dicarboxylic Fc(COOH) 2 showed decrease of j p,a but increase of E 1/2 upon inclusion, suggesting TC4AS preferred reduced form Fc(COOH) 2 to oxidized form Fc + (COO − ) 2 . TC6AS behaved similarly to TC4AS but with larger decrease in of E 1/2 and j p,a . The larger shift of E 1/2 for inclusion of FcCOOH, the oxidative form of which is also neutral (Fc + COO − ), than that attained with TC4AS endorses main role of hydrophobic interaction between TCnAS (n=4, 6) and ferrocenyl guest molecules. Having the most preferential electrostatic interaction, kinetically stable complex was formed between TC6AS and FcCH 2 NMe3+.