Tin Sulfide SnS thin films with different thicknesses (t=100, 200, and 300 nm) were synthesized successfully by thermal evaporation process. The dielectric permittivity $\epsilon$ and ac conductivity $\sigma_{ac}$ were measured at temperatures in the range of 293–493 K and frequencies in the range of 10 kHz–100 MHz. It is found that there are two conductivity mechanisms and hence two activation energies converts to one mechanism with the increase of $t$. The ac activation energy $E_{AC}$ decreases with thickness and frequency. The exponent $s$ shows a progressive decrease with $t$. The results are explained in terms of structural difference by the effect of $t$ and thermal treatment. Few anomalies in dielectric studies were observed near 340 and 440 K, respectively. These points were related to crystalline phase transitions.