Nematic liquid crystal-isotropic liquid transition temperature-composition curves were calculated for the four binary systems between p-azoxyanisole and Schiff bases. The calculation was done by means of equal G analysis, which is one of the thermodynamic treatments reported by Van Hecke. Two Schiff bases with nitro group were chosen as examples of convex upwards transition temperature-composition curves. Two Schiff bases with dimethylamino group were chosen as examples of Concave upwards transition temperature-composition curves. As a result, deviations from linearity, which have been interpreted so far as due to the interaction between the component compounds, were attributed to the differences between the nematic liquid crystal-isotropic liquid transition entropies of p-azoxyanisole and a schiff base.