Deteriorated concrete structures are repaired by means of grouting. In order to evaluate the repair effectiveness two NDT techniques namely seismic tomography and acoustic emission are applied. Using traveling time of elastic waves, structural velocity is estimated. AE activity is monitored along with water pressurization of the permeability test. As a result, contrary to the common expectation that the velocity increase after filling with grouting agent, enormous amount of velocity drop was obtained after repair due to the incomplete developing process of grout material, whereas AE activity showed dramatic decrease after repair. Furthermore after comparison of those results to the quantity of grouting material, it became clear that damage indices based on AE activity exhibited well the actual damage of concrete structures.