The influence of carbon nanotubes (CNTs) in antiferroelectric liquid crystals (AFLCs) is studied using Landau phenomenological theory. A Landau model is developed to describe the effect of CNTs in the mixture of nematic liquid crystal and AFLCs. The effects of CNTs on the AFLCS and the isotropic to chiral smectic-A* (I-SmA*) transition are studied. Theoretical results indicate the decrease of the helical pitch in the SmC* A phase and the decrease of the I-SmA* transition temperature with the increase of the concentration of CNTs. Theoretical results are compared with experimental results.