The subject of this thesis is „Investigate works and conceptual rehabilitation design of masonry building damaged in earthquake“. The building, that is the subject of the rehabilitation is located at Vjekoslava Klaića 27a in Zagreb. It is a cultural and historical asset that used to be a tobacco factory after the rehabilitation it will be used by the Croatian Restoration Institute. In the introductory part of the paper, a review of the existing literature and legal framework related to the reconstruction of earthquake-damaged buildings is given, and the basic data of the building is presented. Then, the damage to the structural and non-structural elements of the building is presented. The results of the experimental testing are shown in detail, and the methods for determination of the mechanical properties of masonry are explained as well as the methods for determining the basic dynamic parameters of the structure. Then, the strengthening methods applied to the building are shown and elaborated in detail. In the practical part of the work, experimental research was conducted on the building. The numerical model in the project of reconstruction was calibrated based on the results of experimentally determined dynamic parameters using the operational modal analysis method. In this way, the reliability of the numerical calculations and ultimately the reliability of the designed reinforcement solutions are increased. At the end of the work, the reinforcements of the building are shown.