Zinc sulphide (ZnS) and silver doped zinc sulphide nanocrystallites (ZnS:Ag) of average size 4 and 8 nm, respectively, have been synthesized by chemical precipitation technique. The structural and morphological studies using X-ray and high resolution transmission electron microscopy (HRTEM) measurements have confirmed hexagonal structure for the samples. Using the impedance spectroscopy method, the effect of grain interior and electrode-sample interface effect on their conductivity have been studied at various temperatures. In high temperature region, the electrode-sample interface effect is found to be larger than that of the grain interior region. Further, the results of the activation energies of the charge carriers in both the regions are determined and analyzed. The conduction mechanism of silver doped zinc sulphide nanocrystallites has been studied at various temperatures and the results are reported.