<p>Today, one of the most serious hazards to the world’s population is drought, which is expected to worsen in many areas due to decreased rainfall and increased evaporation triggered by global climate change. So, a pot experiment was conducted at the greenhouse of National Research Centre, Dokki, Giza, Egypt, during summer season 2023 and 2024 to evaluate the physiological role of chitosan (1 gL⁻¹, 2 gL⁻¹, 3 gL⁻¹) in increasing drought tolerance (60% WFC, water field capacity) of soybean. Results show that drought stress at 60% water-holding capacity (WHC) significantly reduced plant growth, photosynthetic pigments, indole acetic acid, seed yield, and seed quality (oil, carbohydrate, and protein). It also increased phenolic compounds, osmolytes (total soluble sugars, proline, total soluble protein), membrane leakage, hydrogen peroxide, lipid peroxidation, and the activities of antioxidant enzymes (SOD, CAT, and POX), compared with well-watered plants (90% WFC). Conversely, foliar-applied chitosan (1 gL⁻¹, 2 gL⁻¹, and 3 gL⁻¹) improves drought tolerance in soybean plants grown at 60% water-holding capacity (WFC). Chitosan application markedly enhanced growth, yield, seed quality, and physiological responses in both well-watered and drought-stressed plants. Chitosan promoted phenolics, osmolytes, membrane stability, and antioxidant enzyme activity while reducing oxidative stress indicators such as membrane leakage, hydrogen peroxide, and lipid peroxidation. It is obvious that 2 gL⁻¹ chitosan is the most effective treatment. It could be concluded that chitosan act as an eco-friendly biostimulant to enhance drought resilience in soybean by improving physiological, biochemical, and growth traits, offering a sustainable strategy for maintaining crop productivity under water-limited conditions.</p>