•Non-enzymatic antioxidant content, as well as antioxidant enzymes activity increased in plants treated with 100 mM NaC1.•With increasing concentration of Fe2O3 NPs, antioxidant enzymes activity decreased in plants under salinity stress.•Using iron nano fertilizers improves antioxidant defense in Dracocephalum moldavica L. under salinity stress.•Appropriate levels of iron Fe2O3 NPs were able to be used as a source of Fe by Moldavian balm under salinity conditions. The effect of iron oxide nanoparticles (NPs), as a salinity stress modifier, was investigated on plant growth and antioxidant systems in Dracocephalum moldavica L. The results showed that the salinity causes a decrease in leaf area, length and fresh and dry weight of the shoot and root. However, foliar application of iron oxide NPs in the concentration of 60 ppm increased all aforementioned traits. Nevertheless, the interaction between iron oxide NPs and salinity was not significant on the length and weight (dry and fresh) of the shoot and root. Moreover, iron oxide NPs were not efficacious on modifying the effect of highest salinity level on the studied growth characteristics except for leaf area. Spraying the iron oxide NPs significantly increased the leaf area in the plants under salt stress conditions. Total phenolic, flavonoid and anthocyanin content, as well as the activity of guaiacol peroxidase, ascorbate peroxidase, catalase and glutathione reductase enzymes were enhanced in the shoot and root of the plants treated with 100 mM of NaC1 solution. On the other hand, spraying the iron oxide NPs on the plants treated with salinity stress led to an increase in enzymes activities compared to control ones. The results revealed that using iron nano fertilizers improves the antioxidant defense in Dracocephalum moldavica L. under salinity stress.