We have investigated atomic structures as well as growth morphologies of electrodeposited thin Ag and Te films on Au(100) under an aqueous sulfuric acid solution. The extremely flat Ag films were formed by an ideal Frank-van der Merwe mode even at a high deposition rate [similar to 7.2 monolayer (ML)/min], which suggests that the surface diffusion process of Ag adatoms is extremely rapid. In the underpotentially deposited Te on Au(100), the (root 2x root 2)R45 degrees-Te structure (coverage, theta=0.5) for a first monolayer was formed through the (2X2)-Te structure (theta=0.25) under an aqueous H2SO4 solution. In contrast with the Ag films, the bulk deposited Te films were formed by a Stranski-Krastanov mode even at a low deposition rate (similar to 0.5 ML/min), which suggests that the surface diffusion process of Te adatoms is extremely slow. The Te(1010) films (>80 ML) were grown on Au(100) through the c(root 2x3 root 2)R45 degrees (20-30 ML) and (root 2x root 2)R45 degrees-Te(<10 ML) structures.