The Zambezi River Basin (ZRB) faces future challenges in integrated water resourcemanagement (IWRM) due to rapid growth of population and economy. Tools areneeded to support IWRM decision making. A basin wide biogeochemistry modellays a solid foundation for further tool development. In this study, the Soil and Water Assessment Tool (SWAT) was applied to model basin wide biogeochemistry.The model (ZRB1) was calibrated and a local sensitivity analysis conducted. Ni-trogen and phosphorous exporting patterns in the ZRB were analyzed and criticallyevaluated. The prediction quality of ZRB1 in terms of flow and nutrient loadingswas found insufficient. By discussing possible shortcomings of the model, this studyproposed potential ways to increase prediction quality. The conducted sensitivityanalysis revealed interesting mechanics of SWAT such as sensitivities varying overtime and space and a clear dominance of hydrology related input parameters. Thisstudy concludes that SWAT offers a high potential to analyze nutrient flows andtransformations as well as the spatial pattern of biogeochemical cycling within theZRB. Nevertheless, the fact that ZRB1 did not yield reliable prediction qualitymade it not possible to draw solid conclusions on catchment wide biogeochemistry.Proposed next steps are therefore the quality check of input data, the use of a dif-ferent method to calculate surface runoff and the change of hydrological calibrationroutines followed by a chemical calibration of the model.