The host-guest interaction of various mono O-substituted calix[6]arenes, namely, (i) 37-benzyl-38,39,40, 41,42-pentahydroxy-5,11,17,23,29,35-hexa(4-tert-butyl)calix[6]arene (1), (ii) 37-ethylester-38,39,40,41,42-pentahydroxy-5,11,17,23,29,35-hexa(4-tert-b utyl)calix[6]arene (2), and (iii) 37-allyl-38,39,40,41,42-pentahydroxy-5,11,17,23,29,35-hexa(4-tert-butyl) calix[6]arene (3) with [70]fullerene has been studied in a CCl4 medium by the absorption spectroscopic method. All of the complexes are found to be stable with 1:1 stoichiometry. An absorption band due to a charge transfer (CT) transition is observed in the visible region; with increasing ionization potential of the mono O-substituted calix[6]arenes, the peak energy shifts to the higher energy side and the oscillator strength of CT transition increases. Degrees of CT have been estimated by analyzing the CT transition energy as a function of ionization potential. Thermodynamic parameters for the supramolecular complex formation of [70]fullerene with 1, 2, and 3 receptors are reported. The high formation constant value for the [70]fullerene(.)2 complex indicates that 2 forms an inclusion complex with [70]fullerene.