In the field experiment conducted in 2006-2011 at the Experimental Station in Prusy determined were the amount and structure of yield, chemical composition and selected quality parameters of tubers of 6 medium late and late cultivars of edible potato: Jelly, Medea, Niagara, Syrena, Ursus and Zeus. An assessment of variation components was conducted  in order to determine the share of genetic and environmental variation and their contribution to the total variation of the analysed features. Considering the studied potato features the most stable were: the share of marketable tubers, content of dry matter, total starch and protein and a tendency to raw tuber flesh darkening. The share of deformed tubers proved to be the least stable feature. The environmental factors most strongly affected the amount of total and marketable yield, the number of tubers set and their average weight, but also the share of large tuber fraction in yield and the share of deformed tubers. Cultivar properties, to a greater extent than other sources of variability, determined only the content of dry matter in tubers. On the other hand, interaction of cultivars and years of cultivation most strongly determined the contents of starch, total protein, nitrates, tendency to raw tuber flesh darkening and the share of deformed tubers.