In this study, forced vibration tests were conducted on two full-scale substandard reinforced concrete (RC) buildings to obtain the dynamic characteristics (modal frequencies and damping ratios) of these buildings. These tests were carried out before and after quasi-static lateral loading cycles. Through quasi-static cyclic loading, which was applied only in x direction of the buildings, the buildings were forced to experience specific damage states in a controlled manner. The original aspect of the study is investigating the rates of changes of the dynamic characteristics with the increasing damage. According to the test results, it was observed that modal frequencies tend to decrease while damping ratios for different modes tend to increase with the increasing levels of damage. In addition, finite element models of the buildings were established and modal analyses were performed for the undamaged state. Model updating was carried out in order to determine the optimal means of improving the accuracies of the finite element models of the test buildings. Experimentally identified modal frequencies of the buildings and those computed using finite element model were found to be consistent. Since the buildings tested in this study represent most of the existing substandard RC buildings in Turkey, determining the changes in dynamic characteristics with the increasing damage would be useful in the decision of demolishing/retrofitting of these types of buildings after potential future earthquakes.