A passive, wireless and inexpensive sensor has been developed to monitor the conductivity of concrete and thereby provide information on the progress of chloride-induced corrosion of the embedded reinforcement in concrete structures. Sensors are designed to be attached to the reinforcement cages before placement of the concrete in new construction or in portions of rehabilitated structures. Sensors will then be interrogated intermittently over the service life during routine inspections. The results of two experimental investigations are discussed in this paper. In the first, conductivity sensors were submerged in liquids of increasing conductivity. In the second, conductivity sensors were embedded in concrete cylinders and interrogated over a 25-week period during initial set and curing of the concrete. Analysis of the measured data shows that the passive conductivity sensors were successful in detecting a variety of conductivity levels in the concrete.© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.