Metal nanoparticles electrodes present great difference in electrochemical thermodynamics compared with corresponding bulk electrodes, which depends on the size of nanoparticles that construct the electrodes. However, it remains unclear about the influences of particle size on electrochemical thermodynamics of the electrodes. Herein, the size-dependence of electrochemical thermodynamic functions of metal nanoparticles electrodes was deduced theoretically. Experimentally, taking copper nanoparticles electrode as an example, the standard electrode potentials, the temperature coefficients, and the thermodynamic functions of electrode reaction were obtained by determining the electrode potentials of the electrodes constructed by copper nanoparticles with different sizes at different temperatures. Both the theoretical and the experimental results indicate that with the particle size of metal nanoparticles decreasing, the standard electrode potential and surface tension decreases, while the temperature coefficient, the molar reaction Gibbs energy, enthalpy and entropy increase. Moreover, all these physical quantities are linearly related with the reciprocal of particle radius when the radius exceeds 10 nm. Meanwhile, we also found that the influence regularities of particle size on electrochemical thermodynamic functions of metal nanoparticles electrodes are quite opposite to those of oxide nanoparticles electrodes, which is attributed to the nanoparticles being reactant or product in an electrode reaction. (C) 2017 The Electrochemical Society. All rights reserved.