To study the effects of different levels of water stress and nitrogen fertilizer on seed yield and yield components of two common bean genotypes (Phaseolus vulgaris), an experiment in a split plot factorial based on CRBD with four replications was conducted at the research farm of University of Tehran (Karaj-Iran) in 2010. Water stress treatments as the main factor included normal irrigation (60 mm evaporation from open pan), mild and sever water stress (90 and 120 mm evaporation from open pan, respectively) at fourth leaf stage. Nitrogen fertilizer at four levels comprised of zero, 50, 100 and 150 kg N/ha and two red kidney bean genotypes (namely, Akhtar and D81083) were allocated as sub plots in a factorial arrangement. The results indicated that water stress decreased pods/plant, seeds/pod, 100 seed weight, seed yield, total dry matter, harvest index and plant height, significantly (p ? 0.05), but increased seed protein. Nitrogen fertilizer application also increased plant traits, significantly, except for the seeds/pod and harvest index. The two bean genotypes were different in their characteristics excluding the seeds/pod and seed protein content, however, the seed yield was comparatively higher in D81083 than Akhtar genotype. The interaction effects of water stress × genptype on bean seed yield under normal irrigation and severe drought stress was recorded for D81083 and Akhtar genotypes, respectively. Similarly, the interaction effects of water stress × nitrogen on bean seed yield under normal irrigation with 150 kg N/ha and under severe drought stress without nitrogen was higher and lower, respectively