Abstract: Ion-specific stresses of Cl^- and Na⁺ on biomass, growth rate, chlorophyll contents, photosynthesis traits, and ion contents of grain amaranth seedlings were studied and compared under iso-osmotic (-0.096 MPa,-0.198 MPa,-0.437 MPa) salt solutions (NaCl, Cl-salt, and Na-salt) for 10 d in sand culture in a greenhouse. Both -0.096 and -0.198 MPa Cl-salt increased the dry weight of grain amaranth seedlings compared with the control whereas -0.437 MPa NaCl, Na-salt and Cl-salt both significantly reduced plant dry weight. The order of growth inhibition under different treatments with high pressure conditions (-0.437 MPa) was Na-salt > NaCl > Cl-salt. Net photosynthetic rate (Pn), transpiration rate (Tr) and stomatal conductance (Gs) of grain amaranth seedlings in descending order of magnitude suppression was Na-salt>NaCl>Cl-salt treatment. The Na⁺ contents in the leaf were lower those of the stem and root under NaCl and Na-salt stress. Ion selectivity of imbibition or transportation (S_K,Na) in roots, stems, and leaves were all increased under -0.096, -0.198, -0.437 MPa NaCl and Na-salt treatments. In general, growth inhibition of grain amaranth seedlings from Na-salt stress was much more than that from Cl-salt stress. Salt adaptation of grain amaranth seedlings to a certain degree to Na⁺ was due to high K⁺ selective absorption and transport.