Lime is the most commonly used chemical admixture for the treatment of the expansive soils. But the intrusion of sulfate contaminant into the lime treated soil will always results in deterioration of the treated soil. The intrusion of sulfate occurs through acid rains, effluent from tannery industries or mine wastes, intrusion of sea water, construction waste, intrusion of leachate from solid waste fills and sulphate rich groundwater. Therefore, this paper aims at bringing out the effect of sodium sulfate (Na2SO4) solution on the compaction and strength behavior of the lime treated expansive soil. Further, the effect of compaction delay and curing period on the sulfate contaminated lime treated soil is also brought out in this paper. Lime contents of 2.5 (initial consumption of lime (ICL) −1%), 3.5 (ICL) and 4.5% (ICL +1%) were used in this study. The sulfate contamination was limited to 5000, 10000 and 20000 ppm. The experimental results showed that the sulfate contamination decreased the maximum dry density and optimum moisture content of the lime treated expansive soil. Further, the intrusion of sulfate solution into the lime treated expansive soil decreased the strength of the lime treated expansive soil. © 2019, Springer Nature Switzerland AG.