Abstract: Inadequate attention during design and construction of some of reinforced concrete (RC) buildings has been raised questions about the performance levels of these existing buildings under future earthquakes. This study aims to improve seismic design of existing RC buildings under various deficiencies. Total of twelve existing RC buildings in major seismicity zone, Mandalay city, are targeted as case study buildings. Two possible improvement solutions such as steel bracings and RC shear walls are defined as proposed systems in this study. Linear static analysis is carried out for structural stability checking of existing structures based on UBC 97 code. According to the checking results, deficiencies of P-∆ effect are found in three existing pinned based buildings and deficiencies of torsional irregularity are also found in two existing buildings. Firstly, structural improvements under linear static analysis are performed to correct these deficiencies. Then, nonlinear static (pushover) analysis is carried out for performance evaluation of existing structures. Seismic performance enhancement of the proposed existing buildings is evaluated to achieve basis safety objective performance level described in FEMA 356. Results show that RC shear wall is more appropriate not as economic solution for more deficient buildings (Model 8, 10, 11 and 12) whereas steel bracing is effective solution for less deficient buildings (Model 1, 2, 3, 4, 5, 6, 7 and 9).