Sulphur centers in silver chloride crystals are studied by ESR measurements and also observation of their kinetic behaviors. The paramagnetic centers produced by illumination have a symmetry axis of <100> and g values of g//=1.999 and g⊥=2.031. They are ascribed to AgS radicals substituting for AgCl molecules in the crystal. The activation energy of formation of the photoproduced ESR signals is 0.22–0.28 eV, and that of thermal bleaching is about 0.75 eV. These centers are considered as produced by trapping the holes and liberating the interstitial silver ions. The initial sulphur centers are guessed as AgS-Ag+ complexes formed under the condition of excess silver ions. The effects of hyperfine interaction by S33 isotopes are preliminarily described, in which the splitting constants are several gauss in both directions of the main axis of the g tensor.