Brassica napus is often used as a catch crop to deal with the issue of N leaching, but considering that this culture is also characterized by a low N index, prediction of the crop's N uptake capability and N partitioning is required. Based on the kinetic descriptions of N uptake, partitioning and mobilization in every plant organ, the aim of this work was to build up a compartmental model of N dynamics in oilseed rape. The use of kinetic equations of NO3- transport systems, determined by 15NO3O labeling under controlled conditions, combined with experimental field data from the INRA-Chalons rape database were used to model NO3- uptake during the plant growth cycle. The quantitative effects of different variables such as day/night cycle, ontogenetic stages, root temperature, PAR and soil nitrate availability on different components of the Low- and High-Affinity Transport Systems (LATS and HATS, respectively) of nitrate were taken into account. Simulated uptake correlated well with measured data of N uptake under field conditions for contrasted N fertilization rates tested. A second set of experiments was therefore conducted under field conditions where plants were harvested weekly after sequential 15N labeling in order to quantify in each tissue N coming from uptake or derived from mobilization. Logistic and exponential equations were fitted to the N flows for each compartment. Precise study of N flows from leaves at different nodes revealed the existence of two main groups of leaves in terms of their apparent capacity to mobilize N. Thus, N requirements for seed filling were mainly satisfied by N mobilized from vegetative parts (about 73 % of the total N in pods). A complex pattern of N mobilization from the leaves to vegetative or reproductive tissues was then highlighted but a general model was used to test different relevant parameters.