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Isobaric vapor−liquid equilibrium (VLE) data of the mixture of methyl palmitate and methyl stearate at 0.1 kPa, 1 kPa, 5 kPa, and 10 kPa were measured with a modified Othmer still. Methyl palmitate and methyl stearate were the major components of the biodiesel. The experimental results were correlated with Wilson and nonrandom two-liquid (NRTL) activity coefficient models and were compared with a group contribution model (UNIFAC). The binary interaction parameters of the Wilson and NRTL models were fitted into the experimental data which were obtained at different pressures. The UNIFAC model did not predict the VLE for methyl palmitate and methyl stearate at reduced pressures well. The Wilson and NRTL models could well correlate with the experimental data at 1 kPa, 5 kPa, and 10 kPa. However, for the lower pressure 0.1 kPa, the Wilson model and NRTL model had worse correlatations with our experimental data than the higher pressures. These models could develop VLE calculations of the mixtures and provide guidelines for the separation of components by vacuum distillation.