The main objective of the bachelor thesis was to design foundation slab under twelve storey office buliding. Its structural system is designed as a monolithic skeleton complex in the first underground floor with columns with dimensions 500 x 500 mm, concrete core made of walls, which have thickness 250 mm and perimeter walls with the same thickness. The building has horizontal dimensions 18,4 x 23,4 m. Calculation of internal forces was developed by software Dlubal-RFEM5. Foundations was designed by STN EN 1992-1-1 : Design of concrete structures.