Chitosan (Cs) and chitosan nanoparticles (CsNPs) were tested for their ability to alleviate salinity stress in Phaseolus vulgaris L. plants. The study found that both Cs and CsNPs improved plant growth, yield, and biochemical traits under salinity stress (25, 50, 100, and 200 mM NaCl). CsNPs showed more beneficial effects than Cs, reducing oxidative stress markers like hydrogen peroxide, lipid peroxidation, and electrolyte leakage while increasing antioxidant enzyme activities and photosynthetic pigments. CsNPs also enhanced ion homeostasis by reducing Na⁺ content and increasing K⁺ content in shoots and roots. The application of Cs or CsNPs improved total soluble sugars, starch, and total carbohydrates, which are crucial for plant growth under stress. The results indicate that CsNPs are more effective than Cs in mitigating the negative effects of salinity stress on common bean plants. The study highlights the potential of CsNPs as a promising strategy for improving crop productivity in saline soils.Chitosan (Cs) and chitosan nanoparticles (CsNPs) were tested for their ability to alleviate salinity stress in Phaseolus vulgaris L. plants. The study found that both Cs and CsNPs improved plant growth, yield, and biochemical traits under salinity stress (25, 50, 100, and 200 mM NaCl). CsNPs showed more beneficial effects than Cs, reducing oxidative stress markers like hydrogen peroxide, lipid peroxidation, and electrolyte leakage while increasing antioxidant enzyme activities and photosynthetic pigments. CsNPs also enhanced ion homeostasis by reducing Na⁺ content and increasing K⁺ content in shoots and roots. The application of Cs or CsNPs improved total soluble sugars, starch, and total carbohydrates, which are crucial for plant growth under stress. The results indicate that CsNPs are more effective than Cs in mitigating the negative effects of salinity stress on common bean plants. The study highlights the potential of CsNPs as a promising strategy for improving crop productivity in saline soils.