This study was conducted during the years of 2007, 2008 and 2009 in the green house and Laboratory of the Department of Horticulture, Faculty of Agriculture, Suez CanalUniversity, Ismalia, Egypt.This experiment was carried out to study the effect of seed priming under different levels of salinity on seed germination, seedling growth and field behavior of tomato. Under laboratory conditions, low salinity level (1500 ppm) or un saline      (control) recorded maximum values of germination percentage (GP%), germination performance  index (GPT) and coefficient of velocity and minimum values of mean germination time (MGT) , uniformity germination and T50 % and  tallest seedling. Maximum values of fresh and dry weight/ seedling, total carbohydrate, total phenol and peroxidase enzyme activity were also recorded under low salinity level. Seed priming in KCl was the superior treatment for enhancing GP%, GPI, coefficient of velocity, both fresh and dry weight with no significant differences with NaCl with respect to coefficient of velocity. Under green house conditions, low salinity at 1500 ppm significantly increased growth rate, leaf production per week, both fresh and dry weight as well as number of leaves / plant, concentration of chlorophyll a and b as well as carotenoides in leaf tissues of tomato compared with other treatments or control. Seed priming in PEG significantly increased growth rate, leaf production per week, both fresh and dry weight and number of leaves/ plant, concentration of chlorophyll a and b as well as carotenoides in leaf tissues of tomato. The interaction between seed priming and salinity levels showed a significant effect on seedling growth and chemical constituents of germinated seeds of tomato. This study was conducted during the years of 2007, 2008 and 2009 in the green house and Laboratory of the Department of Horticulture, Faculty of Agriculture, Suez CanalUniversity, Ismalia, Egypt.This experiment was carried out to study the effect of seed priming under different levels of salinity on seed germination, seedling growth and field behavior of tomato. Under laboratory conditions, low salinity level (1500 ppm) or un saline      (control) recorded maximum values of germination percentage (GP%), germination performance  index (GPT) and coefficient of velocity and minimum values of mean germination time (MGT) , uniformity germination and T50 % and  tallest seedling. Maximum values of fresh and dry weight/ seedling, total carbohydrate, total phenol and peroxidase enzyme activity were also recorded under low salinity level. Seed priming in KCl was the superior treatment for enhancing GP%, GPI, coefficient of velocity, both fresh and dry weight with no significant differences with NaCl with respect to coefficient of velocity. Under green house conditions, low salinity at 1500 ppm significantly increased growth rate, leaf production per week, both fresh and dry weight as well as number of leaves / plant, concentration of chlorophyll a and b as well as carotenoides in leaf tissues of tomato compared with other treatments or control. Seed priming in PEG significantly increased growth rate, leaf production per week, both fresh and dry weight and number of leaves/ plant, concentration of chlorophyll a and b as well as carotenoides in leaf tissues of tomato. The interaction between seed priming and salinity levels showed a significant effect on seedling growth and chemical constituents of germinated seeds of tomato.