It is known that thiourea selectively forms crystal adducts with 2, 6-dialkylnaphthalenes (DAN). In connection with the application of thiourea adduct for the separation of 2, 6-DAN from the relevant mixtures, equilibrium constants for the formation of thiourea adducts of diisopropylnaphthalene (DIPN) isomers and di-t-butylnaphthalene (DtBN) isomers were determined at temperatures from 273 to 293K. Both recovery and purity of 2, 6-DAN isomers were used to evaluate the separation process. Equilibrium constants for 2, 6-DIPN were determined to be 0.0138 at 273K and 0.0400 at 292K, while those for other isomers of DIPN were found to be more than unity. The order of adduct forming tendency of the DIPN isomers was as follows: 2, 6-DIPN>2, 7-DIPN>1, 7-DIPN> 1, 3-DIPN_??_1, 4-DIPN_??_1, 6-DIPN. In addition, equilibrium constants for 2, 6-DtBN were also determined to be 0.00428 at 273K and 0.00813 at 293K, while those for 2, 7-DtBN were 0.33 at 273K and 0.51 at 293K. These equilibrium constants can be used to evaluate both the yield and the purity of 2, 6-DAN recovered in the adduct which agree well with the observed values with standard deviations of 4.8% for recovery and 3.6% for purity, under the conditions in which studies were conducted. The separation of 2, 6-DAN isomers from the relevant mixtures by multistage thiourea adducts was simulated by the equilibrium model, providing the relationship between the conditions of formation of adduct and the extent of separation of 2, 6-DAN isomers.