Solubility of N-cetylpyridinium perchlorate (CPP) in water–propanol-2 mixed solvent with mole fractions of alcohol x2=0, 0.1, 0.3, 0.5, 0.7, and 1.0 was determined by the isothermal saturation method within the temperature range from 278.15 to 308.15K. The constants of (CP++ClO4 −) association were determined using the conductance method. The solubility products and total standard Gibbs energies, enthalpies and entropies of transfer, ΔGtr 0, of the CP+ and ClO4 − ions from water to the aforementioned mixed solvents were calculated. The results were compared with analogous polythermic data for cetyltrimethylammonium perchlorate obtained earlier, and also with those determined for tetra-n-pentylammonium perchlorate in the present study at 298.15K.