Historic buildings need to be re-functionalized because of environmental factors, economic reasons, sociocultural changes. During the re-functionalization-renovation period, only the seismic performance of the building is analyzed to sustain the historic building according to law and legislation. However, the historic buildings show a considerable energy saving potential. Therefore, the performance assessment of historic buildings requires multidisciplinary approach, which examines both energy and seismic issues. The study aims to demonstrate how the energy and seismic performance improvement of a re-functioned historic building conducted with an integrated approach based on four phases: 1) evaluating the energy performance of the existing building, 2) determining energy & seismic retrofit packages 3) the energy and cost performance evaluation of retrofit packages 4) analyzing the performance of the retrofit measures. A detailed energy simulations used for finding the effects of energy measures that are passive, active, and their combinations by taking into consideration the historical value of the buildings. Life-cycle cost analysis is applied to find the best retrofit strategy for the his torical building case by using the net present value method. The proposed methodology has been applied to a historical building in a Mediterranean City, Izmir to find the best retrofit measures for improving the performance of the building. Results show that the implementation of the external wall and applying the new HVAC system are the most effective measures considering both energy, seismic and cost performance. The study indicates that an integrated approach can improve both energy, seismic and cost performance of the historic buildings.