Üsküdar-Çekmeköy metro line of 20 km having twin tubes is commissioned to Doğuş Construction Company by Istanbul Metropolitan Municipality authorities. During the excavation, Tunnel Boring Machines (TBMs) encountered with complex geology consisting of sandstone, siltstone, shale, limestone, conglomerate, and diabase dykes. Two TBMs having diameters of 6.57 m are used in excavation of Üsküdar-Çekmeköy metro line. In this study, performance analysis is carried out along the tunnel route between Üsküdar-Çarsi stations by analyzing TBM data (thrust, torque, speed of cutter head revolution, advance rate, alarms etc.). Machine utilization time is also determined and, the breakdowns and stoppage times are deeply analyzed to identify their effects on TBM performance. This study illustrates how to... simplify and practically usage of the TBM performance and breakdown data.