The isobaric vapor liquid equilibrium (VLE) data were measured for the binary system (ethane-1,2-diol + butan-1,2-diol) at (20, 30, and 40) kPa using a modified dynamic recirculating still. The thermodynamic consistency of the experimental data was confirmed using the Herington and van Ness semiempirical method. The Wilson and universal quasichemical (UNIQUAC) models were used to correlate the activity coefficients with the liquid-phase composition. The average absolute deviation of the bubble-point temperature and vapor molar fraction for all of the systems obtained from the Wilson and UNIQUAC models are less than 0.18 K and 0.0011, respectively. Furthermore, the binary system (ethane-1,2-diol + butan-1,2-diol) exhibited azeotropic behavior. In addition, the data were calculated using the UNIFAC (Do) model (modified UNIFAC model) in which ethane-1,2-diol was treated as two groups (-CH2OH), and butan-1,2-diol was split to four groups (-CH2OH, -CHOH, -CH2, and -CH3). The new group-interaction parameter for CH2 CH2OH was obtained and used to estimate the VLE data for the binary system (butan-2-ol + butan-l-ol) at 101.3 kPa. The results are consistent with those of the literature data.