The radiosensitizing effect of non-nitro compound S-8712 on HeLa-S,3, cell line was investigated, using cell colony forming assay in vitro. When the concentration of compound was 2 mmol/L, sensitizer enhancement ratio (SER) of hypoxic cells calculated according to the ratio of D,0, and D,q, was 1.04 and 1.26. When the concentration of S-8172 raised to 6 mmol/L SER was 1.35 and 1.25 respectively. It showed that the radiosensitizing effect of S-8712 was less then MISO at same concentratron. The effect of S-8712 was also observed on oxic HeLa-S,3, cells. This compound demonstrated marked inhibition on repair of sublethal damage for aerobic cells.