Selenium and tellurium sensitization centers¹ were characterized by wideabsorption bands with peaks at 520nm and tails ending at 760nm, while fog centers by wide bands extending from 500nm to wavelength longer than 780nm. These results were coincided with that for sulfur sensitization.² The activation energies for the formation of chalcogen sensitization centers were 32.0kcal/mol (S), 34.0 (Se), and 38.2 (Te), while those for the formation of the corresponding fog centers were 39.8kcalimol (S), 29.8 (Se), and 20.7 (Te), respectively. The order of the size of chalcogenide ions is S^2-2-2-. By extending our model for a sulfur sensitization center³ to chalcogen sensitization centers, it is thought that the increase in the size of a chalcogenide ion made it difficult for the ions at lattice sites to move for the formation of the corresponding sensitization center. In addition, the order of activation energies for the formation of fog centers coincided with the order of the Gibbs Free Energies for the formation of the corresponding silver chalcogenide, supporting the idea that a fog center of chalcogen sensitization is a cluster of the coresponding silver chalcogenide.