The conductance data of trimethylsulfonium halides (bromide and iodide) in acetonitrile at various temperatures (25, 30, 35 and 40°C) are presented. The results were construed by applying the Fuoss-Onsager equation to obtain the parameters: equivalent conductance at infinite dilution (Λo), the distance of closest approach (a°) and association constant (KA). After calculation of the electrostatic Stokes' radii (R+ and R-), their sum is likened to a° value. The thermodynamic functions (ΔHo, ΔGo, ΔSo) and the activation energy (ΔEs) were determined; Negative values of Gibbs free energy change ΔGo for trimethylsulfonium halides (Bromide and Iodide) indicate that the association process is preferable than the dissociation process. The positive value of (ΔHo) points to that the association process is endothermic. Entropy change (ΔSo) values were positive which means that the solvation of ion-pair decreases emulated to that of the free ion.