The hole lattice model of rectangular parallelepipeds is presented to describe the structural and excess thermodynamic properties of nematic-non-mesogenic mixtures. The molecular attractions are taken into account within the quasi-chemical approximation. A procedure for evaluating model parameters from data on the thermodynamic characteristics of pure components and the activity coefficients of the non-mesogen at infinite dilution at the nematic-isotropic transition temperature of the mesomorphic component is proposed. The mixing functions (enthalpy and volume), activity coefficient of the non-mesogen and the order parameters of the components are calculated at a molecular level for systems composed of 4-methoxybenzylidene-4′-propylaniline and a non-mesogen (tetrachlormethane, benzene and n-heptane). The calculated results are in quite good agreement with experiment in the temperature rang from 319·2 to 335·4 K.