Dissociation constants (KD) for Ph3C+AsF6– and Ph3C+SbF6– in CH2Cl2 and CH2Cl2–CH3NO2 were determined. The entropies and enthalpies of dissociation in CH2Cl2(AsF6–ΔH–2.2 ± 0.2 kcal mol–1, ΔS–25.1 ± 0.8 cal mol–1 K–1, SbF6–ΔH–2.2 ± 0.5 kcal mol–1, ΔS–25 ± 2 cal mol–1 K–1) are in agreement with the previously determined parameters for SbCl6– anion, taking into account the larger diameter of the latter anion. The values of the Stokes radii of AsF6– and SbF6– ions (both 2.2 Å) as well as the effective interionic distances in both ion-pairs (equal to 7.1 Å) were evaluated. The values of KD increase ca. 102 times at 25 °C on passing from CH2Cl2 to CH3NO2 as solvent. This gives an opportunity to study reactions with predominantly paired (in CH2Cl2) or free (in CH3NO2) cations.