Salinity stress is one of the most important abiotic stresses in arid and semi-arid climates that limit crop plants' growth and development. Salicylic acid
(SA) is an endogenous plant growth regulator that can regulate physiological processes and improve the plant's tolerance to stress. A factorial experiment based on a completely randomized design was carried out to investigate the effects of different levels of SA (۰, ۰.۵, and ۱ mM) on some growth and biochemical parameters of spinach under salinity stress (۰, ۴۰, and ۸۰ mM). Our findings showed that salinity negatively affected growth traits and photosynthetic pigments while SA increased them. For example, under severe salinity stress, a concentration of ۱ mM SA increased shoot length by ۲۳%, and ۰.۵ mM SA enhanced both the fresh and dry weight of the root by ۲۶%. Also, under moderate and severe salinity stresses concentration of ۱ mM SA increased shoot dry weight by ۱۳۰ and ۶۹%, shoot fresh weight by ۵۲ and ۴۲%, chlorophyll a by ۵۳, and ۸۶%, chlorophyll b by ۷۹ and ۱۱۲%, total chlorophyll by ۶۳, and ۹۶%, carotenoids by ۶۳ and ۶۴%, soluble sugars by ۴۴ and ۱۳%, anthocyanin by ۴۸ and ۲۵%, respectively in comparison to the control plants. In conclusion, a concentration of ۱ mM SA decreased negative effects of salinity stress on evaluated growth and biochemical parameters more than ۰.۵ mM, and improved tolerance of the spinach plants to the salinity stress by an increase in plant growth, total chlorophyll and carotenoids, soluble sugars, and anthocyanin.