The use of compounds that can improve plant tolerance to abiotic environmental stress, including salinity, is important. To evaluate the adjustment of salinity stress using humic acid (HA), a factorial layout was conducted based on a complete randomized design with three replications on the Hypericum perforatum L. as an Iranian medicinal plant were collected from Hamadan province in the tissue culture laboratory of the Faculty of Agriculture, Sayyed Jamaleddin Asadabadi University during 2019. Experimental treatments included NaCl as salinity at three levels (such as 0, 50 and 100 mmol.L-1) and HA at four levels (control, 25, 50, 100 mg.L-1). The results indicated that the plants treated with 50 mg.L-1 HA without salinity had the highest germination percentage (98.65), germination rate (38.94) and root length (34.21 mm). The highest plant height, fresh and dry weight of both shoots and roots and total chlorophyll were obtained under control conditions and HA with a concentration of 100 mg.L-1. While the highest amount of phenol in the treatment was 50 mmol.L-1 salinity and HA with a concentration of 50 mg.L-1. In the treatment of 100 mmol.L-1 salinity and HA with a concentration of 50 mg.L-1, the highest amount of total antioxidants (99.77 mg/g FW) and total flavonoids (2.39 mg/Qe g FW) and the lowest amount of hydrogen peroxide (9.12 µg/g FW) were obtained. The results showed that the mitigating effect, especially the application HA of 50 mg.L-1 levels, can affect the physiological processes and morphological traits of the Hypericum perforatum L. under salinity stress.