Chelating agents added to contaminated soils may increase solubility and phytoextraction efficiency of soil metals. However, they can create negative effects on soil biological quality. A 90-day incubation experiment was conducted to evaluate mixed effects of chelating agents and poultry manure on changes in available Cd, Pb and As, CO2-C efflux, microbial biomass C, dissolved organic C (DOC), and N mineralization in metal-polluted agricultural soil. Application of poultry manure resulted in a considerable increase in soil pH, DOC, CO2-C efflux, net N mineralization, net N nitrification, and microbial biomass C compared to those in unmanured soil. Availability of arsenic increased twice in manure amended soil due to changes in pH and DOC. However, adding poultry manure did not affect the concentrations of available Pb and Cd compared to those in control soil. Chelating agents increased CO2-C efflux, DOC, and metal availability but decreased microbial biomass C and net N mineralization. Maximum decrease in microbial biomass C, net N mineralization, and net N nitrification, was observed in EDTA applied soil possibly due to high metal availability to soil microorganisms. Overall results revealed that the application of synthetic chelators in combination with poultry manure enhances available As and demonstrates better environment for soil biota.