The use of nitrogen-fixing bacteria reduces the use of synthetic nitrogen fertilizers. However, salt stress can negatively affect the establishment of biological nitrogen fixation (BNF). In this context, the aim was to evaluate the use of brackish water at different phenological stages on the gas exchange and mineral composition of inoculated and non-inoculated peanut crops. The experimental design used was completely randomized, following a 5x2 factorial arrangement, with four replications, using five irrigation strategies with brackish water with an electrical conductivity of 5.0 dS m-1 applied at different phenological stages of the crop: E1 - at 14 days after sowing - DAS (vegetative stage); E2 - at 25 DAS (flowering stage); E3 - at 36 DAS (gynophore emergence stage); E4 - at 46 DAS (pod formation stage); and E5 - control, and inoculated and non-inoculated plants. The earlier the salt stress is applied, the lower the gas exchange in the peanut crop, with more significant effects up to 36 DAS, the phase of gynophore emergence and elongation, so plants inoculated with rhizobia show greater efficiency in the use of brackish water. Similarly, from 36 DAS onwards, leaf mineral content decreases, with the exception of sodium, which increases. It is recommended to use brackish water associated with the use of Bradyrhizobium spp. in the pod formation stage of the peanut crop.