New protein-based biopolymer introduced in this study to stabilize soil. Since the conventional soil stabilization materials, especially cement, have harmful effects on the environment, alternative eco-friendly materials, caseinate salt biopolymer have been used in this study to reduce environmental concerns. Casein and sodium caseinate biopolymer obtained from milk added to soil, and mechanical properties of biopolymer treated soil were investigated through a series of laboratory tests. The effects of biopolymer content, curing time on improving soil were studied by unconfined compression test. The caseinate is added to the soil at different percentages(0,2,4,6 amd 8%) and the liquid limit, omc and mdd, ucs were determined. The results showed that compressive strength of biopolymer treated soil was increased when the curing time had passed, and biopolymer content increased. On the whole, the protein-based biopolymers propose a strong potential as additives for soil treatment rather than some material such as cement and chemical polymers.