The first two steps of the preparation of Ag-O-Cs photocathodes are the deposition of silver films and their oxidation with the glow discharge method. The fractal structure and texture structure in the silver oxide thin film have been characterized by transmission electron microscopy (TEM). The Hausdorf dimension D of the fractal structure is calculated to be 1.80 +/- 0.01. The formation mechanism of the fractal structure is also discussed.