The measurement of vapor-liquid equilibrium of n-propanol and isobutanol binary mixture was carried out in a condensed vapor phase recirculating still at atmospheric pressure. The experimental data were checked by Herington consistency test and chi-square distribution of statistics. The correlation results showed that van Laar equation was the most suitable model to describe the VLE behavior of this mixture and that the absolute correlation coefficient of the pair parameters of model is near to unity. This says that the model parameters are linearly related to each other and this mixture behaves like a regular solution. The experimental points with large residuals were deleted from the data set. The F-distribution test of statistics was then applied to judge whether the new data-set could better describe phase behavior of mixture than the previous set. The statistical chi-square analysis was also applied to determine whether the estimated variance of fit used for objective function was reasonable. The data treatment applied in this study was different from that applied to isoprene and n-pentane mixture in our previous paper (Lee et al., 1994) where the T-x diagram was used to delete the experimental points with systematic error.