The effect of a water-soluble extract from natural materials on radiation-induced mutations was studied by means of TSH assay in Tradescantia 4430 stamen hair cells. Inflorescence cuttings, with or without pretreatments of natural extracts for 3 hours, were exposed to 1 Gy of gamma ray. Comparisons were made on the basis of pooled data during the peak interval between the mean pink mutation frequencies of the experimental groups. Pretreatments of FB or FB-I resulted in about two-fold increases of the pink mutation frequencies, compared to those of the control group. Synergism between certain fractions and radiation was a possible cause of the increased DNA damage. FB and FB-I had a radiosensitizing effects on the pink mutations in Tradescantia 4430 stamen hair cells (p<0.001). On the other hand, the extract PP in a proper concentration significantly reduced the pink mutation frequencies (p<0.05). The result means that PP has a protective effect on the radiation-induced cell damage.