To determine the changes of nitrogen contents in the leaves and seeds of common bean (Phaseolus vulgaris L.) genotypes under contrasting moisture regimes, two field experiments were conducted as split-plot in a randomized complete block design with four replications. Two levels of irrigation (irrigation after 55-60- and 100-110-mm evaporation from class A pan, respectively) and eight genotypes including white beans (WA45021 and WA4531-17), red beans (Akhtar, D81083 and AND1007) and Chitti beans (KS21486, MCD4011 and COS16) were studied in the main- and sub-plots, respectively. Leaf nitrogen (N) and proline contents were measured at two growth stages (pre-flowering and pod filling period). Grain yield, seed N and seed protein contents were measured at harvest. The results indicated that white beans had lower leaf N and seed protein contents than red and Chitti beans under both irrigation regimes. Under drought conditions, AND1007 and COS16 showed markedly higher levels of accumulation of leaf N and proline. Seed protein was higher in Chitti beans. Water deficit reduced the leaf N by 19% and 28% at two growth stages and grain yield by 39.8%. By contrast, proline content of all genotypes was increased by 105%. Seed N and protein contents had the lowest reductions under drought, while increasing N and proline contents in the leaves increased grain yield under this condition. Besides, lower values of seed N and protein is associated with higher yields of genotypes. Totally, based on the grain yield, red beans were more drought-susceptible than white and Chitti groups.