The Flory-Huggins model has been modified to predict the phase behavior of asphaltene precipitation process by adding solvents such as n-C5, n-C6 and n-C7 to an oil sample. The adjustable parameters of this model are calculated by optimization of an objective function and experimental data of asphaltene precipitation. The amount of asphaltene precipitation has been calculated based on the modified Flory-Huggins model compared with the Flory-Huggins model and the experimental data of references. It is shown that the modified Flory-Huggins model can accurate predict the asphaltene precipitation. Also, the differential solubility parameters of asphaltene and oil at different proportions of solvent have been calculated. The results show that the values of this parameter increases when solvent ratio enhancement. (c) 2005 Elsevier Ltd. All rights reserved.