Abstract: The soil mixing technologies (SMT) such as stabilization/solidification (S/S) and ground improvement (GI) are used to treat heavy metal and organic-contaminated site soils in the Castleford, Yorkshire site, UK. The ground granulated blastfurnace slag (GGBS) and magnesia (MgO) are used in this study. The unconfined compressive strength (UCS) tests as well as the BS EN12457 batch leaching tests are conducted on the S/S contaminated soils at 1.5 years and GI soils at 1 year to assess the influences of different depths on the strength and leaching performances of these samples. The results show that the MgO-GGBS can significantly improve the strength of contaminated soils as the average UCS of MgO-GGBS-treated samples exceeds 350 kPa suggested by the UK design standard. Moreover, except part of Ni, the leaching concentrations of Cu and Pb are able to meet drinking water standard of the England. The combination of MgO and GGBS are found to be able to immobilize Ni efficiently. Compared with the GI technique, the S/S technique can achieve higher pH, lower leaching concentration of both Ni and organic compounds, which is more effective in immobilizing heavy metals and organic compounds. The depth of the site has few influences on the properties of contaminated soils after remediation.