Similar to the work done by Kambour et al. and ten Brinke et al., an effective interchange energy parameter epsilon(eff) is introduced into the calculation of binodal curves for random copolymer systems according to the Revised Freed (R-F) model previously established by Hu et al. for homopolymer system. epsilon(eff) is a function of chain composition and various pairs of energy parameters. For contrast, the Flory-Huggins (F-H) model has also been extended to study random copolymer system in the similar way. In order to check the validity of this kind of approach, the calculated results have been compared with the corresponding MC simulation data. It is shown that the results obtained by R-F model are quite consistent with MC simulation data while that by F-H model shows large deviation due to the excess mean-field approximation employed. (c) 2005 Elsevier B.V. All rights reserved.