Abstract: The chemical structure of Pingyangmycin (PYM) is identical with that ofBleomycin A_5. We prepared ~(99m)Tc-PYM for clinical evaluation. Using the im-proved stannous chloride reducing method with no N_2, the effects of pH, stirringtime, Sn~(2+) and PYM concentrations were studied. The relations between theselabeling conditions (except stirring time) and the biodistribution in the tumor-bearing mice are here reported. The results indicate that the optimum conditions for ~(99m)Tc-PYM labelingare: pH 5. 0-6.2, SnCl_2 concentration of 0. 1-0. 4 μg/ml and PYM 0. 5mg/ml ormore than 0. 5mg/ml. The labeling yield of 96. 7(±0. 3)% is higher than before(94% with N_2). It was found that 1.5 hours after injection the tumor uptake wasthe highest (except kidney tissue). and better than those described in previousreports. Therefore we suggest that the ~(99m)Tc-PYM prepared with these labelingconditions may be offered on clinical trial for tumor positive imaging.