Comfort is one among several aspects in building design. Comfort of the occupant can be measured from the dynamic performance of the building during earthquake. This performance can be increased by installing vibration control to reduce dynamic responses of the building. Considering the space-use efficiency, the building is utilizing certain floors to act as mass dampers. The floors are able to move back and forth independently to counter building vibration. Utilizing an existing floor slab as a mass damper is known as passive vibration control or in particularly named self mass damper (SMD). A 14-story reinforced concrete building is modeled as a case study. The movable floor placement is varied in 3 configurations. The modeled building is excited by El Centro 1940 and Denpasar 1979 ground accelerations, independently. The study compares the dynamic responses of building without SMD and with SMD in three different placements. Placing SMD in 4 top floors (13th,12th, 11th, 10th) gives the best result in reducing building’s dynamic response compared to SMD in 4 mid-height floors (11th,10th, 8th, 7th) or separate group (13th, 12th, 6th, 5th). It is shown that the building has a tendency to response conforming 1st mode of the building. From the analysis, it can be concluded that applied SMD system gives greater reduction on building’s displacement, velocity, and acceleration in response to Denpasar ground acceleration rather than El Centro 1940.