Winter oilseed rape cultivars (open-pollinated variety, four composite hybrids, one restored hybrid and the CMS ogura line) were tested during two crop seasons of 2002/2003 and 2003/2004 in field trials at two locations in western Poland. The objectives of the present study were: to determine the variability of yield and the most important phenotypic traits of different types of winter oilseed rape cultivars and to analyse the genotypic variability of this cultivars by environment interactions. The growing seasons differed especially in terms of water supply. Seed yield, yield components and some quality traits (oil content and total glucosinolate content) were recorded. The tested cultivars showed substantial differences in terms of yield and other investigated traits. Analysis of variance indicated that the main effects of cultivar and locations were significant for all the traits of the study. Very high heritability estimates were obtained for seed yield (0.90-0.98), yield components (length of silique, number of seeds per silique and weight of 1000 seeds), and also for oil and glucosinolate contents. The correlation coefficients between the investigated traits display strong positive relationships between seed yield and the number of seeds per silique, chlorophyll content, and the length of flowering period. The results confirm the higher productivity of hybrid cultivars, as well as their better adaptability to variable environmental conditions, especially drought.