Magnetostrictive sensors (MsS) provide a noncontact means to transmit and detect elastic waves in a ferromagnetic material. This paper reports results of using MsS for the evaluation of debonding between seven-wire prestressing strands and concrete. Two MsS configurations are described. One uses a coil that encircles the strand, and the other does not. The advantage of the encircling coil is higher sensitivity; the advantage of the other is that it can be operated from the concrete surface and does not necessarily require removal of concrete. The results showed a correlation between signal attenuation and bond quality. The guided wave speed was also found to be inversely proportional to the bond quality.