Abstract. The saturated vapor pressure of ethacrylic acid solutions in acetonitrile and acetic acid was measured by a static tensimetric method in the temperature range of 295-355 K. The composition of the equilibrium phases as well as the activity coefficients were received from the experimental measurements of the temperature-dependent saturated vapor pressure. We then used the temperature and concentration dependent activity coefficients to calculate the excess thermodynamic functions of the solutions mixing (H E , G E , S E ).