Drought stress is a factor that affects plant growth and development, both in terms of morphology, anatomy, and physiology. Mutant Oryza sativa L. strain 51 of Cempo Ireng cultivar as the result of gamma-ray irradiation is superior mutant black rice strain which has a faster planting period of 10-20 days than its control and shorter plant height. This study aims to determine the morphological, anatomical, and physiological responses, especially the proline content inside the leaves of mutant black rice strain 51. The study used a completely randomized design (CRD) with the treatment of drought stress using PEG 6000 in Yoshida liquid media. The seedlings were planted for 21 days in untreated media, then treated for 14 days. Observation of morphological characters was carried out by measuring plant height, root length, leaf area, and plant biomass. Observations of anatomical characters were carried out by observing the cross-section of the root. Observation of physiological character was carried out by measuring leaf proline levels. The results showed that drought stress with PEG 6000 inhibited the growth and development of mutant rice strain 51. Drought stress reduces plant height, root length, leaf area, plant biomass and the area of root aerenchyma. Proline leaf content increased significantly at a PEG concentration of 30%. Mutant rice strain 51 showed a tolerant response to drought stress with the significant increased of proline, the increased of root stele diameter and the constant number of metaxylem.