The arthrodire placoderm, Dunkleosteus sp., is reported from the Upper Devonian (Frasnian) of the Holy Cross Mountains, Poland. The material comprises partially preserved remains of two individuals found in the Kellwasser-like horizon of the Płucki locality. The remains are preserved as broken bone fragments redeposited from shallower environment into deep-shelf conditions. They are labelled as Dunkleosteus sp. and seem similar to Dunkleosteus marsaisi from the Famennian of Morocco. It is likely that the form from Poland represents a new species that requires further collecting and study of new specimens. The described specimens are the oldest occurrence of the genus Dunkleosteus in Europe, the most complete one from Poland and one of the biggest placoderms with a head about 60 cm long.