Expansive soil covers large areas in a variety of regions in Jordan which is insufficient to meet the engineering specifications in construction. Phosphogypsum is considered to be the main by-product material which comes from phosphate rock deposits that is available in Jordan. The main purpose of this research is to study the effects of stabilization by phosphogypsum on expansive soil properties. Three Jordanian regions were chosen to represent the expansive soils, Irbid, Madaba, and Abu-Nusire city. Soils were mixed with phosphogypsum at different percentages by dry weight of soil. Some of the representative laboratory tests for swell properties were conducted: grain size distribution, plasticity limits, standard compaction test, swell pressure and others. Laboratory results showed a positive response in the engineering soil properties which were confirmed by the Jordanian specifications for the sub-grade soils which may be used in road and building constructions. A 20% to 30% of phosphogypsum by weight of dry soil was found suitable to improve the engineering soil properties, such as the decrease in clay content and changed in classification from A-7 and A-6 soils to A-6 and A-4 soils, respectively. Field tests on short sections of roadways treated with phosphogypsum under a low to medium sustained traffic are recommended.