Abstract: The biodistribution of 99 Tc m MIBI and 99 Tc m GSH in mice bearing breast cancer EAC and sarcoma S 180 , nude mice bearing osteosarcoma are studied. The results show that no radioactivity concentrates on tumor site for 99 Tc m MIBI, and radioactivity is concentrated on liver, heart and bladder. Radioactivity ratios of tumor to nontumor tissues (T/NT) are less than 1.0 except blood,brain and spleen. The uptake percentage of radioactivity per gram tissue in mice bearing EAC and S 180 tumor at 15 and 90 minute after injection is of 1.48, 1.08, 2.52 and 1.09 %ID/g for 99 Tc m MIBI; and 1.46,0.80,2.33 and 0.94 %ID/g for 99 Tc m GSH, respectively. Tumor imaging is clear and T/NT is greater than 1.0 for most organs for 99 Tc m GSH at 6 h after injection. The tumor uptake percentage of radioactivity per gram tissue is of (0.12~0.21)%ID/g. It indicates that 99 Tc m MIBI concentrates less radioactivity on osteosarcoma, but 99 Tc m GSH can accumulate on breast cancer, sarcoma, osteosarcoma and may be applied for tumor positive imaging.