Metal contaminations (Pb, Zn, Cd) in soil are concerned due to their human health and ecological risks. In-situ phosphate treatment that immobilizes soil metals may be a prospective remedial alternative for reducing the threats of contaminated metals. Laboratory and field studies were conducted to assess the metal risk reduction and determine the chemical species transformation by soluble phosphates in contaminated urban soil. Smelter-contaminated soils in Joplin City, within the Jasper County Superfund Site, southwest Missouri, were treated with phosphoric acid at rate of 10g P kg-1 under laboratory and field conditions. Soil samples were collected after two-month treatment, respectively, and analyzed for in-vitro bioavailability, leachability, and chemical fractionation of the metals. Results have indicated a significant risk reduction and species transformation of the metals by the treatment, which would effectively reduce potential threats of contaminated metals to human health and ecosystem. The risk reduction is accomplished by transforming the metals from labile to insoluble species as induced by the in-situ soil treatment. This study would verify the effectiveness of in-situ phosphate treatment as a potential remedial alternative for safeguarding human and environment from metal contamination.