Salinity is one of the most important abiotic stresses that affect plant growth and development. In order to study the effects of salinity stress on oat (Avena sativa L.), salinity treatments including 0 (control), 50, 100, and 150 mM sodium chloride and nitric oxide in form of sodium nitroprusside in three concentrations (0, 25 and 50 µM) were applied. The changes of chlorophyll  fluorescence were analyzed using the JIP-test. Results of this experiment showed that concentrations of 50 and 100mM of Nacl did not have a remarkable effects on chloropyll a fluorescence. Significant increase in chlorophyll a fluorescence was observed in highest salinity (150 mM of Nacl). Furthermore, results of this study also revealed that the application of nitric oxide van alleviates the harmful effects of salinity on photosynthetic electron transport chain where application of sodium nitroprusside in concentration of 50 mM, led to decrease in chlorophyll a fluorescence intensity compared to non-treated plant under salinity stress.