The severity of seismic damage of reinforced concrete buildings depends on the tectonic characteristics of area, seismic features of ground motion, quality and quantity of buildings. One of the most important factor"s, affecting the seismic damage, is the degrading rate of building. Degradation of stiffness and strength are the parameters, which their effect on the seismic damage of buildings are investigated, using an inelastic dynamic analysis. The buildings which are studied are moment resisting RC frames. In order to study the inelastic dynamic behavior of these buildings, IDARC software is used. Based on the obtained results, 40% degradation of strength or 50% degradation of stiffness will cause severe structural damage in the buildings.