To investigate the impact of nitrogen (N) mineral on reproductive potential of Brassica napus L, plants were treated with different levels of N treatment (N0; N100; N500). The half of N content for each treatment were applied at the beginning of the early vegetative stage and the rest was applied at the late vegetative stage. Nitrogen content in plant tissues such as root, stem and branch, leaf, pod and seed was analyzed and harvest index (HI) was calculated as percentage of seed yield to total plant weight. Biomass and nitrogen content were significantly affected by different levels of N supply. Biomass was significantly decreased by 59.2% in nitrogen deficiency (N0) but significantly increased by 50.3% in N excess (N500), compared to control (N100). Nitrogen content in all organs was remarkably increased with nitrogen levels. N distribution to stem and branches, and dead leaves was higher in N-deficient (N0) and N excessive plants (N500) than in control (N100). However, nitrogen allocated to seed was higher in control (N100) than in other treatments (N0 or N500), accompanied by higher HI. These results indicate that the optimum level of N supply (N100) improve HI and N distribution to seed and excessive N input is unnecessary.