Abstarct: Salinity stress, as one of the most critical and widespread abiotic stresses globally, affects over 20% of the world's cultivated agricultural land. Serotonin and dopamine, due to their unique characteristics as two important antioxidants, improve plant tolerance to environmental stress factors. This study aimed to evaluate the effects of different concentrations of serotonin (0, 50, and 100 µM) and dopamine (0, 100, and 200 µM) on the physiological and biochemical traits, as well as diosgenin content, in fenugreek under 200 mM salinity stress. The results showed that salinity stress significantly reduced pigment content and auxin levels while increasing antioxidant enzyme activity, cell wall vulnerability, hydrogen peroxide and nitric oxide content, proline, flavonoid, phenol, soluble sugar, and diosgenin content. The simultaneous application of 200 µM dopamine and 100 µM serotonin under salinity stress increased superoxide dismutase, polyphenol oxidase, catalase, ascorbate peroxidase, guaiacol peroxidase activity, phenol, flavonoid, soluble sugar, proline, and potassium content by 94%, 270%, 182%, 145%, 162%, 127%, 123%, 195%, 278%, 183%, and 270%, respectively, compared to plants under salinity stress without these stimulants. The application of 100 µM serotonin under salinity stress reduced nitric oxide, chlorine, and sodium content by 35%, 43%, and 63%, respectively, compared to untreated plants under salinity stress. The findings confirmed that the application of 200 µM dopamine in plants under salinity stress reduced chlorine, sodium, and nitric oxide content by 40%, 46%, and 45%, respectively, compared to untreated plants. The highest exxpression levels of the SMT, CAS, SSR, and SQS genes were recorded as 24, 18.33, 20, and 19, respectively, under salinity stress with the simultaneous application of 100 µM serotonin and 200 micromolar dopamine (Compared to the non-use of these two stimulants and the absence of salinity stress). Moreover, the separate application of 200 µM dopamine and 100 µM serotonin under salinity stress increased diosgenin content by 170% and 111%, respectively, compared to untreated plants under normal conditions. The results of this study confirmed that the external application of these two stimulants synergistically modulates photosynthesis, the biosynthesis of osmoprotectants, the enzymatic and non-enzymatic antioxidant defense systems, secondary mextabolites, hormonal responses, and the maintenance of reactive oxygen species homeostasis to reduce the adverse effects of salinity stress in fenugreek.