In this study, a sensor for detecting corrosion of rebar embedded in reinforced concrete structures was fabricated and its performance was verified. In order to monitor the open circuit potential(OCP) of the rebar embedded in reinforced concrete, a concrete embedded solid electrode was constructed as a sensor using MnO2. The OCP of the rebar could be observed using a sensor and a data logger. The decrease of the OCP to -510mV (vs.MnO2) or less was judged to be corrosion of the rebar. Since it is a solid-mediated sensor, it is more stable and durable than an electrode using an aqueous solution, and it is considered that the corrosion state of the rebar can be monitored for a long period of time.