Structural assessment of four storey office and store building with basement, made of reinforced concrete at Chalandri region. The main reason for conducting this structural assessment study is the installation of steel mezzanines at the top level of the first and second storeys and change of the operational use of specific parts of the building. Furthermore, the structural integrity of the abovementioned steel mezzanines (plan area 60 sq.m. each) was examined individually. The members of the steel mezzanines are installed at the perimetric reinforced concrete members of the building. The following requlations and standards are applied: 1. National Intervention Code, 2. Eurocode EC0 (Basis of Structural Design), 3. Eurocode EC1 (Actions on Structures), 4. Eurocode EC3 (Design of steel structures). The analysis and the structural checks of the building were conducted with Fespa 22 v.8.3.0.16 software, while the structural assessment of the steel mezzanines was carried out with ETABS software, of CSI company.