Tuned-Mass dampers, if well-tuned to a particular natural frequency, are an 
attractive solution in reducing excessive vibrations of buildings subjected to strong 
and unpredictable earthquakes. Two important parameters greatly affect the building
seismic response are the input energy to the building and the dissipated energy of
the structure. The optimum design is one that minimizes the difference between
these two energies. This research aims to evaluate the effects of Tuned- Mass
dampers on energy dissipation. Tuned mass dampers dissipate a great amount of 
energy. Without their existence, this energy would damage the building or disturb
the occupants. Analysis of a ten-story reinforced concrete building with and without 
TMD using ETABS software is carried out. The tuned mass damper is placed on top
of the building. The dynamic response of structures due to earthquakes is greatly
reduced when tuned mass dampers are used. Results indicate the increase in mass of 
the TMD enhances the R.C building response to seismic vibrations.