System identification was performed to two RC high-rise buildings located in Tokyo, Japan, one was 37 stories and the other was 32 stories. Response analysis was conducted to the 37-story building for which there was structural data available. The strong motion data of the buildings that recorded the successive earthquakes: before, during, and after the mainshock of the 2011 Off the Pacific Coast of Tohoku Earthquake were used as input in system identification to obtain dynamic parameters. The parameters as results of system identification were then used as input data in response analysis to observe the behavior of the MDOF model under some earthquake motions and to determine the adequate damping type that governs the behavior. Health monitoring was conducted as a combination of system identification and response analysis to monitor the more specific part of the building. The dynamic parameters of the buildings after the mainshock were changed compared to that before the mainshock, the frequency decreased to 24%, the period increased to 32%, and the damping factor increased to 50%. The adequate damping types of the MDOF model before the mainshock were modal damping and Rayleigh damping, while that during the mainshock were proportional damping to initial stiffness and proportional damping to nonlinear stiffness. The structural members were in a good condition before the mainshock, but the stiffness degradation occurred when they were struck by the mainshock, the story shear force exceeded its cracking capacity but still below the yielding capacity, with maximum ductility 0.4, it happened to almost the entire structure except the 4 top stories. The decreases of frequency on the upper and lower part of the building were 15% and 18% respectively that indicates the stiffness degradation on the lower part was higher than that on the upper part.