Abstract: The activity coefficients f of naphthalene in the aqueous salt solution were determined at 25 ℃ by spectrophotometer. The salts used are LiBr, NaBr, KBr, NH_4Cl, NaF and KF.When lgf is ploted vs. c_s for these salts, the results obtained are all straight lines The salting-out constants κ were calculated.We have calculated the salting-out constants of naphthalene in six aqueous salt solutions by the formulas of (1) Debye-McAulay, (2) Conway-Desnoyers-Smith, (3) McDevit-Long, (4) scaled partical theory, (5) modified Bockris′ dispersion energy theory and (6) modified internal pressure theory. In the systems having ions and nonelectrolyte molecules both of large size, the effect of dispersion forces can not be neglected. Modified Bockris′ theory indicates signs of salting-out effect correctly. For large nonelectrolyte molecules, the equation of modified internal pressure theory gives results in better agreement with the experiment than others.