Differences in nitrogen (N) use efficiency and their physiological basis among different rape (Brassica napus L. ) varieties were studied using N efficiency coefficient, i.e. the ratio of seed yield in N stress condition to that in normal N supply in a pot experiment. Results showed that there were significant differences in N use efficiency (NUE) among five rape varieties, with NUE coefficient varying from 0.37 to 0.69. Under N stress condition, the variety 231 was high NUE variety with the highest seed yield and NUE coefficient, but the...