One of the major goals in the field of rehabilitation and renovation of existing structures is to determine mechanical properties of materials as well as their level of damage, namely the presence of defects, cracks, weathering effects, etc., by means of non-destructive (NDT) techniques. NDT tests, in fact, are easier and more economics than destructive ones because they do not necessitate sample extraction and preparation; furthermore they are often the unique way to assess the material properties in case of historic and architectural buildings, where the possibility of extracting core samples is limited or not possible. The ultrasonic pulse velocity testing has been proved to be a useful and reliable non-destructive test for assessing the compressive strength and the elastic modulus of concrete in existing structures. Furthermore, the use of both ultrasonic tests and Schmidt hammer tests allow to have a good estimation of concrete compressive strength (SONREB method) by reducing the influence of the variables affecting the two technique when used alone. Both the technics have also been suggested to investigate mechanical and physical properties of rocks, but further experimental data are needed to confirm the reliability of the method. The present work is a part of a wider research aimed at set up non-invasive diagnostic procedures for the mechanical analysis and qualification of the ancient masonries; it is specifically devoted to verify the effectiveness and/or to point out critical aspects and limits of the above mentioned non-destructive tests - already applied in the field of concrete and compact stones -with reference to the characterization of soft stones