The study on the response of common bean genotypes to rhizobia inoculation and effects of P and N on biological nitrogen fixation was carried out in field and Screen house experiments. Field experiments arranged in a split-split plot design were conducted to (a) Screen 16 common bean genotypes for capacity to fix nitrogen when inoculated with Rhizobium inoculants and (b) Assess genotype by environment interaction (G x E) on biological nitrogen fixation. The locations were the main-plot, two rhizobia inoculants Biostacked, Nitrosua and control as sub-plot, and 16 common bean genotypes as sub-sub plot factor. A Screen house experiment was carried out in factorial arrangement with rhizobia inoculant at three levels as one factor, and two levels of Nitrogen and Phosphorous (with and without) as second and third factor respectively and three common bean genotypes namely Kablanketi, Rojo and G51105-A as fourth factor. This resulted to 36 treatment combinations replicated three times. The results from the field experiments revealed high significant difference (P < 0.05) among genotypes and genotypes x environment interaction. Inoculation had significant effect in measured variables such as nodule number and dry weight per plant, seed percent nitrogen content, shoot ureides concentration. Biostacked inoculant was found to be superior compared to Nitrosua. Genotypes which showed promising results in nodulation included Lyamungu 85 closely followed by Pesa, Zawadi, Seliani 97, Rojo, Kablanketi and Carioka, indicating good adaptability for nodulation trait across the locations. Screen house experiment revealed that inoculation using either rhizobia in combination with application of Phosphorous increased nodule number, nodule dry weight, root dry weight, shoot and seed nitrogen. Therefore, Commercial production of rhizobia inoculants should be explored in the country since use of inoculants has shown good results. Farmers should also be advised to use P-fertilizers as this will increase BNF and a consequence increase in yield.CRSP