Application of soluble phosphates is emerging as a cost-effective remediation technique for immobilizing Pb and reducing the risk of contaminated soil. The impact of the phosphate treatment on soil microbial communities that sustain the terrestrial ecosystem and soil productivity is largely unknown and has been insufficiently evaluated. This study was conducted to assess the alteration of soil microbial properties induced by in situ phosphate treatments in Pb contaminated soil under field conditions. Soil samples were collected from contaminated urban site treated with phosphoric acid using three methods of application: Surface applied, Pressurized injection, and Incorporation with roto-tilling, in the Jasper County Superfund Site, MO. The samples were characterized for microbial biomass by total organic carbon (TOC) and enzyme activity by acid/alkaline phosphatase assays. Total organic carbon (TOC) gradually increased over time regardless of treatments, with a slightly more rapid increase for the treated over the control (78% vs. 60%). Enzymatic activity measured had a similar trend as TOC, with a higher increase for the treated than the control (15% vs. 13%) over 2-years period. Results suggest that reduction of soil Pb risk can be achieved by phosphate treatments without alteration of soil microbial growth and activity.