Bean (Phaseolus vulgaris) is a globally important legume crop valued for its nutritional content and adaptability. Establishing a robust root system during early growth is critical for optimal nutrient uptake, shoot development, and increased resistance to biotic stress. This study evaluated the effects of exogenous indole-3-butyric acid (IBA) on root and shoot development in two bean cultivars, Onceler-98 and Topcu, during the seedling stage. IBA was applied at four concentrations: 0 (control), 50, 100, and 150 μM. Morphological parameters measured included root length (RL), root fresh weight (RFW), root dry weight (RDW), root nodule number (RNN), shoot length (SL), shoot fresh weight (SFW), and shoot dry weight (SDW). The experiment followed a randomized complete block design with four replications. Significant (p ≤ 0.05) and highly significant (p ≤ 0.01) differences were observed across treatments and cultivars. The results indicated that Onceler-98 generally responded more favorably to IBA application, with optimal growth performance observed at 100 μM. In contrast, Topcu was less responsive to IBA overall, and high concentrations—particularly 150 μM—tended to suppress nodule formation.