Symbiotic nitrogen fixation is a process in which nodulebacteria use the molecular nitrogen from the atmosphere and through enzyme called nitrogenase transform it into a form that can be used for the plants. In many soils, nodulebacteria are often not suitable or not in sufficient quantities. In such conditions there is a need for inoculation of seeds or soil with highly efficient strains of nodulebacteria. Different enviromental factors affect the process of nodulation and nitrogen fixation. The application of mineral nitrogen fertilizers can suppress this natural process of fixation. The aim of this study was to determine the impact of fertilization with different rates of mineral nitrogen on nodulation and the symbiotic effeciency of indigenous Bradyrhizobium japonicum strains. In the vegetation pot experiment two indigenous B. japonicum strains, isolated from different regions of Croatia and one reference strain as well as different rates of mineral nitrogen were tested. Based on the obtained results, significant differences were found for some investigated traits depending on the applied strain of nodular bacteria and the concentration of the applied nitrogen. It was determined that the application of increased rates of mineral nitrogen has impact on reduced mass of dry matter and the number of nodules. The highest nitrogen content in the plant was determined for plants that were inoculated with indigenous B. japonicum strains without the application of mineral nitrogen.