Increasing activities in the environmental management of nuclear wastes incite significant interest in the study of the interaction of actinides with organic matter in aqueous solution, especially at elevated temperature. The system U(VI)-acetic acid is studied in aqueous solutions at pH 2 in the temperature range from 15 degrees C to 55 degrees C by affinity capillary electrophoresis (ACE). The formation of two complex species UO2CH3COO+ and UO2(CH3COO)(2) is observed. Thermodynamic parameters (the molar Gibbs energy of reaction (Delta(r)G(m)), the molar enthalpy of reaction (Delta H-r(m)) and the molar entropy of reaction (Delta S-r(m))) are determined at fixed ionic strength of 0.05 mol center dot L-1 (NaClO4-HClO4) and calculated at 0 ionic strength with extended Debye-Huckel equation for the activity coefficients. Obtained results are compared with literature data. (C) 2013 Elsevier Ltd. All rights reserved.