Abstract: An aqueous-based inoculant composition in liquid form for leguminous seeds that produces an immediate nodule formation and an increased nitrogen fixation, containing microorganisms of the Rhizobium or Bradyrhizobium genus, a molybdenum compound selected from alkali metal molybdates and a compound that neutralizes the seed exudates, which are toxic for the bacteria, selected from polymers of compounds presenting an amide, amine or imine moiety. The inoculant composition remains stable at room temperature, keeping the number of viable bacteria over long periods of time and ready to be used.