The Middle Palaeolithic site Ketrosy (Middle Dniester valley) has been found and investigated by N.K. Anisyutkin in 1974–1979. He excavated 3 different complexes. The most interesting complex is the area № 1. It has the one (third) cultural layers in fair preservation, which had been dated appr. 100,000 years ago, by buried soils investigations. In the obtained collection, the hammerstones are represented by 19 pebbles with the traces of pecking. By its metrics, tools from Ketrosy fit within the framework of variability of the Middle – Upper Paleolithic hammerstones. But the location of the impact-marcs does not look ordinary and we suppose the transverse grip of the tools, conditioned, perhaps, by the anatomy of the inhabitants of the Ketrosy site. Low intensity of wear indicates “ad-hoc” mode of pebbles use as hammers. Spatial analysis of stone artifacts and bone remains (in particular – the context of hammers findings) confirm the short occupation and well-defined objects of cultural layer.