Winter oilseed rape (Brassica napus L.) is distinguished by poor nitrogen (N) efficiency but heavy N balance surplus. Cultivation of oilseed rape hybrids has been suggested as an important strategy to enhance the N efficiency and to reduce the large N balance surpluses in this crop, but the underlying physiological mechanism remains not well understood. In this study, seed yield and N efficiency parameters of an oilseed rape hybrid and its parental lines were investigated under contrasting N fertilization levels over three site-years. Seed yield-N uptake relationships were analyzed by quantile regression fitting a logarithmic model to both the 99th yield quantile and the whole data set. The maximum achievable yield (Yield(MAX)) of the hybrid was greater than the parental lines at a wide range of N uptake levels; in addition, the gap in yield between Yield(MAX) and actual yields for the hybrid was smaller than for its parents, indicating higher yield stability against environmental stresses. At both low (0 kg N ha(-1)) and high N (180 kg N ha(-1)) supply, the hybrid accumulated more N, which contributed to the yield heterosis. The higher seed yield of the hybrid was also related to the higher N utilization efficiency at the high N rate, which was attributed primarily to the improved N harvest index (NHI), but there was no genotypic difference in seed N concentration. Further analysis of seed N origins highlighted the importance of leaf and stem N remobilization other than post-flowering N uptake for genotypic variation in NHI at high N supply. These results suggest heterosis in seed yield and stability as a consequence of higher maximum yield attainable at a wide range of N uptake levels and smaller yield gaps. A higher capacity of N uptake contributed to the yield heterosis regardless of N levels. Additionally, efficient leaf and stem N remobilization also contributed the yield heterosis at high N supply.