We investigated the viscoelasticity of aqueous threadlike micellar solutions of a cationic surfactant, cetyltrimethylammonium bromide (CTAB), and additives, sodium p-toluenesulfonate (NapTS) and sodium salicylate (NaSal). The dependence of the rheological longest relaxation time (tau (m)) on a molar ratio of pTS(-) relative to that of Sal(-) in the interior of threadlike micelles was mainly discussed. The value of tau (m) was dependent on the ratio and also on the total concentration (C-S*) of free pTS(-) and Sal(-) anions in the bulk aqueous phase at C-S* < 30 mmol kg(-1). On the other hand, the value of tau (m) in the solutions with the molar ratio in the micellar interior higher than 0.5 exhibited the same C-S* dependence at C-S* > 50 mmol kg(-1) as observed in a threadlike micellar system formed by CTAB and NaSal. These imply that the entanglement relaxation mechanism in the threadlike micellar system is influenced by both the microstructure of the threadlike micelles and the C-S* values.