Tvrđa in Osijek was suffered a strong earthquake in 1964. However, all the buildings survived the earthquake only slightly damaged or even undamaged. Of course, at the time of its construction there were no aseismic regulations. The earthquake causes the horizontal load to the building walls, which are resisted by the shear strength. The aim of this paper is to determine the actual mechanical properties of historical heritage buildings in Osijek. Tested masonry unites (solid clay bricks) were originall from Tvrđa. The compressive strength of masonry units and lime mortar were estimated according to current regulations. The wall specimens were made using prescribed lime mortar so to be considered as filled. Masonry shear strength characteristics were obtained for nine test specimens subjected to cyclic loading. Test results were recording by computer. Data were processed using Microsoft Excel.