This study was conducted to investigate the salt tolerance of five cotton genotypes [three Gossypium hirsutum L. (DN 1, DP 491, and FM 989) and two G. barbadense L. (Cobalt and Pima S-7)] under NaCl or Na2SO4 salinity conditions at similar osmotic potentials (100 mM NaCl vs. 70 mM Na2SO4 and 150 mM NaCl vs. 111 Na2SO4). To investigate whether the addition of calcium sulfate could alleviate the deleterious salinity effect, two more treatments were prepared by adding 10 mM CaSO4 to 150 mM NaCl and 111 mM Na2SO4 solutions. All genotypes had significant growth reduction in all salt treatments as compared to their respective controls. Whereas Upland and Pima cotton did not differ in response to salt, DP 491 had lower growth reduction as compared to other genotypes and was therefore more salt tolerant. Salt type did not affect the growth of FM 989 and Pima S-7; however, dry weight (DW) of all organs were reduced to a greater extent by NaCl than by Na2SO4 in most organs in Pima Cobalt, shoot and total DW in DP 491, and root DW in DN 1. The addition of CaSO4 alleviated some detrimental effects in DN 1 caused by NaCl and in Pima Cobalt caused by Na2SO4. The five genotypes also responded to salt treatments differently in that DN 1 and DP 491 had higher Na+ and Cl- concentrations and higher leaf osmotic potentials than the other three genotypes except for higher Cl- concentrations in Cobalt. These results indicated that diversity of salt-tolerant mechanisms existed among the five cotton genotypes.