To explore the possibility to employ 99mTc-MIBI to monitor biological response of tumor cells after irradiation and to observe the relation between the radiation doses and the uptake levels of 99mTc-MIBI in tumor cells, the cells were irradiated with a single dose of 2 Gy, 10 Gy and 20 Gy respectively. The uptake of 99mTc-MIBI in each dosage group was determined before and 24, 48, 72 h after irradiation respectively. Apoptosis index (AI), plating efficiency (PE) of tumor cells was simultaneously determined. There was a positive correlation between uptake levels of 99mTc-MIBI and AI(r = -0.91, P < 0.05). A negative correlation was noted between the uptake levels and PE (r = -0.86, P < 0.05). It is suggested that 99mTc-MIBI may be used as a tracer to monitor the change of viability state of tumor cells after being irradiated with different doses.