A sandwiched 15 nm AgOx thin film of the super-resolution, near-field optical disk was studied using a confocal Z-scan system. Nonlinear optical properties of quartz glass/ZnS-SiO2 (170 nm)/AgOx (15 nm)/ZnS-SiO2 (40 nm) were measured using a Q-switch Nd : YAG pulse laser of wavelength 532 nm, pulse width 0.7 ns, and 15.79 kHz repetition rate. Transmittance and reflectance of the sandwiched AgOx thin film show important optical responses at the focused position of Z-scan. The dissociation processes of AgOx, recombination of the silver and oxygen, and the resonance of the localized surface plasmon of the nano-composites of the AgOx thin film are correlated to transmittance and reflectance at the focused position of the Z-scan for different input laser powers. An irreversible upper threshold intensity of 4.40 x 106 mW cm-2 at the focused position was found. A reversible working window of the focusing intensity between 1.86 x 106 and 4.40 x 106 mW cm-2 was measured with sandwiched AgOx thin film alone. The near-field interactions of the AgOx thin film and the recording layers of super-resolution near-field optical disk are also discussed.