A number of methods have been developed for measuring the capacity and efficacy of antioxidants, but there is no simple and universal measurement method. In this chapter, the electrochemical monitoring of antioxidant capacity is introduced. The antioxidant capacity of foods was monitored by two different methods using electrochemical measurement. One was the electrochemical measurement of food constituents that can easily be oxidized by electrochemistry. The other was the electrochemical measurement of food constituents that were oxidized by radicals. The antioxidant capacity obtained from these two different methods was associated with the capacity evaluated by assay of DPPH, ESR, and vitamin C. The electrochemical measurement was performed by USB-powered portable potentiostats and disposable screen-printed electrodes. This system for electrochemical monitoring of antioxidant capacity can be easily extended to the development of a hand-held monitoring system.