The objective of this study was evaluated the effect of two isolates of Pseudomonas, with low (ENA 4413) and high (ENA 4419) antagonistic effect to R. leguminosarum bv. phaseoli strains, on the development of common bean plants co-inoculated with a strain BR 10049. The experiment carried out in sand, showed that inoculation of common bean plants with only these rhizobacteria increased of root and leaf area as well as the total dry matter of the 20 days-old plants. Similar results were observed when common bean plants were co-inoculated with these two rhizobacteria and the strain of Rhizobium BR 10049. An increase of the number of nodules, dry mass of nodules and total dry mass was observed as compared with plants inoculated only with the strain BR 10049. However, there was a decrease of the nitrogenase activity with the co-inoculation of the rhizobacteria mainly with the isolate ENA 4419 that has shown high antagonistic effect to strain BR 10049. Nodules formed solely by rhizobia strains were pink while they appeared greenished when rhizobacteria were coinoculated. The presence of the rhizobacteria was confirmed by plate counting and fluorescence production when nodules were exposed to UV light. Light microscopy sections from nodules originated from the co-inoculation with rhizobacteria showed a small amount of infected cells. These cells were not fully occupied by the bacteroids and in addition they were not enclosed in a membrane envelope (peribacteroidal membrane). In general, the bacteroids appeared free in the host cell.