The relative viscosity-concentration curves ofsodium dodecyl benrer.esu!fon~e (SDBS), ;MgClz. LiCI. NaCl. iNalSO_. and NaI solutions YS water and of :MgCl,, LiCI. N&I. :Na,SO,. and Nal in SDBS solutions with concentrations of 0.298,0.454 and 0.617 mol dmm3 vs the surfactant solution, and the maximum relative viscosity values and corrs5ponding concentrations of f BaCl z, :AICI, and :LaCI, in SDBS solutions with concentrations of 0.298. 0.454 and 0.617 mol dm -' vs the su&ctant solution have been determined respectively at 298.2 i 0.2 I(. The thickening efficiency of inorganic salts is remarkable lor concentrated SDBS solutions. When the salt concentr-*ions are lower. the thickening efficiencies of various salts are in the following orders: :MgCI, a NaCl > LiCl and Nal > NaCl > iNa,SO,. However. when the salt concentration reaches a certain value. SDBS forms a precipitate with the sal: and the thickening ability of the salt :eaches its limit. The maximum relative viscosity values of the SDBS solutions in the presence of various salts are markedly difierent, the orders being LiCl z $MgCI, z NaCl and !Na,SO j > NaCl > Nal. The difierences diminish as the SDBS concentration increases. These results are interpreted in terms of the structure of the micelle solution. electrostat 2 *interactions between ions and micelles. ionic hydratability. changes in the water structure and an activity product e&t.