This paper presents a structural damage diagnosis technique by means of vibration signature analysis. Because Strain Mode Shape (SMS) will reflect the internal force distribution in a structure, any damage that resulted in the change of the latter will be shown in the former. The magnitude of the changes is related to the severity of the internal force redistribution. In most structures force redistribution is the greatest around the damaged zone, therefore the location of damage is implicitly identified by the severity of the SMS change. Two steel model frames were tested in laboratory to verify the sensitivity of this technique when subjected to different types of damage. Test results show that location of damage in a structure can be found by using this approach.