This study evaluates the effectiveness of potassium sulphate (K2SO4) fertilization under salt stressed conditions on physiological and biochemical characteristics and sugar contents of two soybean cultivars (Pioneer and Jack). The treatments including 0 mM K2SO4, 9 mM K2SO4, 0 mM salinity and 90 mM salinity were tested in combination with both cultivars of soybean. Analysis of electrical conductivity, photosynthetic parameters, gas exchange parameters, antioxidant enzymes, malondialdehyde (MDA), sugar contents and glutamine synthetase activities were measured. The results depict that salinity negatively affected the growth, physiological and biochemical attributes of both soybean cultivars, but application of potassium induced salt tolerance in soybean cultivars as the production of MDA contents and electrolyte leakage decreased, while growth parameters, chlorophyll contents, antioxidant enzymes, gas exchange characteristics and sugar contents were improved relative to control plants under saline environment. However, the cultivar Pioneer was more responsive to K2SO4 fertilization as it showed minimum production of MDA contents while maximum antioxidants, gas exchange parameters and sugar contents as compared to Jack. In crux, the salt tolerant cultivar Pioneer was better in utilizing potassium as compared with salt sensitive variety Jack under salt tolerant environment and could be used effectively under salt-affected soils.