Reflectance monitoring of an optical fiber micromirror system was studied as an in-situ liquid phase corrosion sensor. The approach was tested by measuring corrosion rates of Cu in oxygenated sulfuric acid. The measured rates were reproducible and agreed quite well with parallel quartz crystal microbalance measurements and with literature values. The optical fiber system was also used to measure corrosion rates of Cu in saturated ammonium sulfate solutions in which different concentrations of oxygen were dissolved by purging the solutions with gases containing varying partial pressures of oxygen, PO, (total pressure 1 atm). Corrosion rates for the Cu in ammonium sulfate were found to show first order dependence on the dissolved oxygen concentration in the regime (0.0 ≤ PO ≤ 1.0 atm) and compared favorably with literature data for similar conditions.