The complexive ability of p-sulphonato-calix[4]arene towards dioxovanadium(V) and dioxouranium(VI) has been evaluated in acidic aqueous solution (pH 2) using UV–Vis spectrophotometric technique. The results showed that the ligand is capable to complex with the oxo-cations by 1:1 cation to ligand ratios. Formation constants of both systems have been determined at different temperatures (25 to 45°C). Considering the formation constant values, the binding selectivity of the ligand towards the oxo-cations at 25°C is in the order VO 2 + >UO 2 2+ . The thermodynamic parameters have evaluated and are interpreted in terms of the importance of the various interactions responsible for the complexation. A roughly linear relationship between ΔH o and TΔS o has been observed for the studied systems and those were reported in the literature. Finally, the host and guest desolvation involved in the complexation processes are discussed.