To improve the quality of Tc-99m-methylenediphonate (Tc-99m-MDP) for skeletal imaging, different composed Tc-99m-MDP complexes were prepared with addition of antioxidants such as ascorbic acid, getisic acid, and p-aminobenzoic acid. To characterize the different Tc- 99m-MDP preparations, some physical and biochemical properties of Tc-99m-MDP such as thermal stability, lipophilicity and bin-dability to serum protein were studied and organ distribution pattern of these complexes also compared. The therma1 stabilities of Tc- 99m-MDP contained antioxidants were dependant mainly on pH, temperature, and elapsed time after the preparation. Tc-99m-MDP complex contained gentisic acid as antioxidant was extremely unstable at alkaline condition. The most stable Tc-99m-MDP was found in the presence of p-aminobenzoic acid. Tc-99m-MDP complexes with antioxidants were very lipophilic but lipophilicity differences in antioxidants were not observed. The bindability of Tc-99m-MDP te serum protein was not affect at pH 5.0∼9.0 by the different antioxidants. However, protein binding percentage of Tc-99m-MDP with ascorbic acid was relatively low (22.7%) at pH 9.0. In biodistribution studies in mice, bone to muscle ratios of Tc-99m-MDPp preparations containing ascorbic acid, gentisic acid, and p- aminobenzoicacid were 15.3, 24.5, and 30.1, respectively Im to our results, p-aminobenzoic acid is fond to be the moat promising antioxidant.