Abstract: Tissue distribution of UO₂²⁺ in mice was investigated with dose of 5 mgU/kg and different chelating agents. A thermodynamic equilibrium model, involved in major metal-ions, low molecular weight molecule ligands and chelating agents, was made to analyze the speciation of UO₂²⁺ in human fluid. Computer simulation indicates that UO₂²⁺ will easily exist as (UO₂)₂(OH)DTPA^2- species when the presence of DTPA and UO₂²⁺ in the blood of mice can be significantly removed out, but to some extent will damage kidneys and bones at same time. In contrast, ascorbic acid prevents ordinary metabolism of uranium in kidneys of mice, without any effect on removal of uranium, unfortunately, the complex compound of UO₂²⁺ ion with ascorbic acid is (UO₂)₂(OH)Ascorbate²⁺ which will affect UO₂²⁺ normal removal from kidneys. It can be concluded that NTA has a little effect on removal of uranium in tissues and organs of mice and promote the UO₂²⁺ and PO₄^3- ion from solid phase as (UO₂)₃(PO₄)₂·4H₂O which will deposit on the bone surface.