A hydroponic experiment was carried out to investigate the effect of immersion durations (1 and 2h) of hydrogen peroxide on roots of strawberry (Fragaria x ananassa Duch.) grown under NaCl stress at (0, 34 and 68 mM NaCl). Roots immersion into H₂O₂ increased plant growth, photosynthetic pigment concentration, leaf relative water content and the activity of antioxidant enzymes i.e. (catalase, peroxidase and polyphenoloxidase) as well as decrease electrolyte leakage compared to untreated plants. High NaCl salinity level, induced ultrastructural alterations in leaflet mesophyll cells such as swelling thylakoids, disintegration of grana staking, increase number of plastoglobuli and starch grains as well as increase the size and number of mitochondria and its structure, shrinkage the plasma membranes, increase the Myelin-Like, membrane vesicles formation and increase the thickness of cell wall. In addition, roots immersion into H₂O₂ led to maintain the chloroplast structure, grana staking and increase the size of chloroplast and mitochondria, decrease the number and size of starch grains and plastoglobuli, decrease the number of membrane vesicles and peroxisomes, as well as maintain the cell wall structural and reduced its thickness. Furthermore, the high NaCl level led to increase the number of stomata and stomatal density and decreased the dimensions of stomatal pore. On the contrary, roots immersion into H₂O₂ decreases the stomatal density and its number. Concerning the leaflet anatomy, it was found that low NaCl salinity level increased the dimensions of midrib region, main vascular bundle as well as the thickness of palisade parenchyma. While, high salinity level, in most cases, decreased all these parameters. In conclusion, immersed roots of strawberry plants (pre-treatment) in H₂O₂ (1.0 M) for 1h application before exposure to salinity stress increased plant resistance and mitigated the deleterious effects of NaCl on cellular organelles.