<p>Water scarcity is one of the major abiotic stresses that affects morpho-physiological parameters, among others, and reduce the productivity of sunflower (<i>Helianthus annuus</i> L.). The roots are considered the most important organ in the adaptation of crops to water stress because they have the ability to modify its architecture, and that response is modulated by phytohormones. We aimed to evaluate and compare the morphological parameters and phytohormonal profiles of two inbred lines of sunflower with contrasting response to water stress, subjected to this stressor and treated with exogenous brassinolide bioregulator during early vegetative growth stage (V4). Seeds of sunflower inbred lines were sown in pots containing a mixed substrate. The treatments were: 1- Hoagland’s solution (control); 2- 265 mM mannitol solution (water stress). Exogenous 0.01 µM brassinolide solution was applied on control and water-stressed seedlings. At V4 stage, the evaluated parameters included roots fresh and dry weight, main root length and endogenous phytohormone levels. The water stress treatment had a negative effect on different morphological parameters such as the main root length. The brassinolide application significantly enhanced morphological parameters in response to water stress such as fresh and dry weight of roots. Also, increased the levels of stress-phytohormones (jasmonic, abscisic acid) and growth-phytohormones (cytokinins, auxins) under water stress. Our findings pointed out the brassinolide concentration used in this study can be a suitable strategy to alleviate the detrimental effects of water stress on the growth of sunflower seedlings through improving the morpho-physiological parameters.</p>