In photosynthetic microorganisms, a series of electron carriers (such as flavodoxin) with the similar function to ferredoxin are expressed following the adverse reduction of ferredoxin under stress conditions. Fld gene reduces disorders of abiotic stresses in the electron transfer processes of photosynthesis. In order to investigate the morphological characteristics of transgenic walnuts harboring Fld ‎gene under salinity stress, a factorial experiment was conducted based on completely randomized design with four replications. In this experiment, transgenic Persian walnut plants expressing Fld (L2, L3, L13 and L17) and ‘Chandler’ as control under different levels ‎of NaCl ‎ (0, 100, and 200 mM) were evaluated under in vitro conditions. According to the results, L13 had the maximum number of healthy leaves (1.14), callus diameter (1.36mm) and number of regenerated leaves (1.13) using 200 mM NaCl. Transgenic lines maintained their natural growth in mild stress after 35 days under 200 mM NaCl, while non-transgenic plants showed injury symptoms in this treatment. In vitro studies showed that the transfer of Fld gene to Persian walnut ‘Chandler’, which is a salt-sensitive plant, improved its growth traits under salinity stress.