Meningoccocal disease constitutes a serious problem in public health. In Brazil about 5,000 cases are notified per year. Outer membrane vesicles (OMV) from N. meningitidis B expressing iron regulated proteins (IRP) is the basis for the development of the respective vaccine. Considering that phosphate is related to bacterial growth, metabolic pathways, polysaccharide and proteins generation, in order to enhance OMV yield production, modifications in original Catlin medium (with iron restriction) were studied modifying phosphate concentrations. Cultivations were carried out in 6 L bioreactor with two extreme initial phosphate concentration values: one of them reproducing the original concentration in Catlin medium (0,83 g/L) and another, two-fold higher (1,66 g/L). Process conditions comprised: 36ºC, 0.5 atm, overlay air flowrate of 1 L/min, agitation varying from 250 rpm to 850 rpm and dissolved oxygen control set at 10% of saturation condition, 20 cultivation hours. Biomass was determined by optical density (O.D.) at 540 nm. Glycerol, lactate, pH, and dissolved oxygen were measured from samples taken out during cultivation. OMV concentration was determined by Lowry method after ultracentrifugation. IRP presence was verified by SDS-PAGE electrophoresis. The increase of phosphate concentration in cultivation medium, at studied range, has influenced negatively bacterial growth and OMV production. In assays with two-fold phosphate concentration final O.D₅₄₀.reached 2.425 and OMV concentration 93.3 mg/L, whereas in the assays without incresed phosphate concentration the antigen yield was almost 50% higher: O.D₅₄₀ reached 4.950 and OMV concentration 142.5 mg/L at the end of culture. These results suggest that phosphate concentration must be maintained in the same concentrations as the original Catlin medium in order to enhance OMV production from Neisseria meningitidis serogroup B cultivations.