This study aimed to investigate the role of arbuscular mycorrhizal (AM) fungi on biological N fixation in Vachellia seyal and transfer of fixed N2 from V. seyal to intercropped Sporobolus robustus under greenhouse conditions. Both plants were grown individually in pots to prevent root contact (“Solid barrier” treatment) or together in two-compartment containers delimited by a plexiglass plate with holes either covered with a 30 µm nylon mesh allowing only hyphal connections between plant roots (“Mesh barrier” treatment), or without nylon mesh allowing hyphae and roots to intermingle (“No barrier” treatment) in a low-nutrient soil. Both plant species were inoculated with the AM fungal Rhizophagus irregularis IR27 strain (“Myc+” treatment) or not inoculated (“Myc-” treatment), whereas all V. seyal seedlings were inoculated with a rhizobial strain Ensifer sp. LCM 4579 (“Nod+” treatment). The 15 N isotope dilution method was used to determine the amount and proportion of atmospheric N fixed by V. seyal (%Ndfa) and the total fixed N that was transferred to intercropped S. robustus. Mycorrhizal inoculation factor had a significantly effect on plant growth parameters and shoot N concentration in V. seyal, but not in S. robustus. The estimated proportions of N fixed by V. seyal was higher in Myc¿+¿treatment (65%) than in Myc- treatment (42%) as well as for the amount of fixed N. About 14% of fixed N were transferred to S. robustus from AM fungal links, whereas N transfer via exudation plus transfer through mycorrhizal network reached 19.5%. The implications of these results are discussed.