Soybean seed is a major source of high-quality protein and oil for human consumption (Katerji et al. 2001). The unique chemical composition of soybean has made it one of the most valuable agronomic crops worldwide (Thomas et al. 2003). Its protein has great potential as a major source of dietary protein. The oil produced from soybean is highly digestible and contains no cholesterol (Essa and Al-ani 2001). Growth, development and yield of soybean are the result of genetic potential interacting with environment. Soybean seed production may be limited by environmental stresses such as soil salinity (Ghassemi-Golezani et al. 2009). Minimizing environmental stress will optimize seed yield (Mc Williams et al. 2004). Soil salinity, resulting from natural processes or from crop irrigation with saline water, occurs in many arid and semi-arid regions of the world (Meloni et al. 2004). The UNEP (United Nations Environment Program) estimates that 20% of the agricultural land and 50% of the cropland in the world is salt-stressed (Yan 2008). Most of the salt stresses in nature are due to Na+ salts, particularly NaCl (Demirel 2005). High salinity lowers water potential and induces ionic stress, and results in secondary oxidative stress. It severely limits growth and development of plants by affecting different metabolic processes such as CO2 assimilation, oil and protein synthesis (Nasir khan et al. 2007). Plants vary tremendously in their ability to tolerate salinity (Bischoff and Warner 1999). The term halophyte means “salt tolerant plant” but is used specifically for plants that can grow in the presence of high concentration of Na+. Plants that can not grow in presence of high concentration of Na+ salts are called glycophytes (Brevedan and Egli 2003). Soybean is classified as moderately salt sensitive instead of moderately salt tolerant (Katerji et al., 2000). Salt tolerance of plants may be dependent on growth stage, varieties, nutrition and environment (Bischoff and Warner 1999). Netondo et al. (2004) reported that photosynthetic activity decreases when plants are grown under saline conditions leading to reduced growth and productivity. The reduction in photosynthesis under salinity can be attributed to a decrease in chlorophyll content (Jamil et al. 2007) and activity of photo-system ΙΙ (Ganivea et al. 1998). Salinity can affect chlorophyll content through inhibition of chlorophyll synthesis or an acceleration of its degradation (Reddy and Vora 1986). Fluorescence of chlorophyll reflected the photochemical activities of photo-system ΙΙ (Ganivea et al. 1998). Photochemical efficiency of photo-system ΙΙ (fv/fm) could be reduced by salinity stress (Jamil et al. 2007; Netondo et al. 2004).