In search for less toxic and more effective radio−sensitizer, the effects of CGEONA (carboxy−β− phenyl−vinyl−germanium sesquioxide sodium salt)on radio−sensitivity of tumor−bearing mice and normal mice were investigated. Radiosensitizing experiment was performed using T−739 mice. The tumor model was LA−795 pulmonary adenocarcinoma, and the effect was assessed using tumor regrowth delay. Radioprotection experiments were performed using Kunming mice. The 30−day survival rate and effects on hemopoietic system were observed. It was shown that the average sensitization enhancement ratio (SER) of CGEONA was 1.4 with 1/10 LD,50 ,drug dosage. The radioprotection experiments showed no significant differece between treated mice and control mice for survival rate and hemopoietic system. Thus, CGEONA shows great potential as a new type of radiosensitizer with less toxicity and more effectiveness. It has no radiosensitizing effect on normal mice and is worthy of further studies.