Using the combination of Flory–Huggins theory of isotropic mixing and Landau theory, we discuss the crystal – rotator-I – rotator-II phase transitions in the binary mixture of alkanes. The influence of concentration on the order parameters and the transition temperatures is discussed. Theoretical results show the first order character of both the rotator-I to crystal and rotator-II to rotator-I phase transitions in the mixture of alkanes. A good agreement between theoretical and experimental results are presented in this paper.