Abstract: A systematic investigation on the solidification/stabilization effectiveness of industrially heavy-metal contaminated soils by a sustainable steel-slag-based binder (BOFS) is introduced. The activation method of the BOFS is explored, and the heavy-metal immobilization effectiveness is used as an evaluation standard. The results demonstrate that the activation of BOFS with monopotassium phosphate (MKP) can significantly improve the heavy metal immobilization effectiveness. The activated-BOFS (PAB) with a MKP/BOFS ratio of 2%~4% obtained from wet mixing and 20 °C drying is found to possess superior performance. Furthermore, the leaching and strength properties of the PAB-stabilized soils are investigated, and the original BOFS is selected as a control binder for comparison purposes. It is also found that the addition of PAB increases the pH of soils, but reduces the toxicity leaching concentration of Pb, Zn and Cd. Also, the addition of both the original BOFS and PAB increases the unconfined compressive strength (q_u) of the stabilized soils, but the activation of BOFS induces a relatively weaker increase in q_u. Overall, this study demonstrates that the sustainable PAB binder has positive effects on the immobilization of the heavy metals and strength increase of the stabilized soils.