Investigations of temperature behaviour of the mean refractive index n, ordinary noand extraordinary nerefractive indices, and birefringence Δn have been carried out for three homologues of 4-n-alkyl-4’-cyanobiphenyls (n = 8, 10, 12). The principal polarizabilities α0and αe, effective geometry parameter αegand average polarizability αavehave been calculated using the isotropic internal field model (Vuks approach). Temperature behaviour of the order parameter in regions of thesmectic A–nematic,nematic–isotropic liquidandsmectic A–isotropic liquidis discussed. All of the optical and orientational parameters, which have been obtained in this work, are in good agreement with the theoretical approach.