To evaluate the quantity of Spirulina cultured in seawater, salt-tolerant strains were screened out and their growth and antioxidant accumulation were studied in different salt concentrations Salt tolerance of five Spirulina strains were investigated with modified Zarrouk medium (with 200-800 mM NaCl). All strains grew well with 400 mM NaCl; their growth rates were almost same as in the control medium. Spirulina strains FACHB-843 (SP843) and FACHB-972 (SP972) had the highest salt tolerance their growth rates in 600 mM NaCl were nearly same as the control. Both strains produced more carotene, phycocyanin, polysaccharides, proline and betaine in 400-600 mM NaCl than the control. Salt stress also induced them to produce higher activities of superoxide dismutase and peroxidase. Total antioxidant capacities of SP843 and SP972 peaked at 600 and 400 mM NaCl, respectively. Spirulina strains cultured with seawater accumulate more bioactive substances and will have a higher nutritive value.