The root extracts of a Chinese herb, Polygonum multiflorum Thunb., have been used for centuries as an internal medicine to improve liver and kidney functions. In this study, we evaluated the antimutagenic property of this drug with the Tradescantia micronucleus (Trad-MCN) assay. The Trad-MCN bioassay is a well-established test for chromosome damage induced by physical or chemical agents in terms of micronuclei (MCN) frequency. Inflorescences of the Tradescantia plant cuttings were first exposed to 0.35 Gy soft X-rays (80 kV, 5 mA, 1 mm Al filter, dose rate around 0.50 Gy/min), followed by drug treatments at 1, 3, and 6% concentrations of the aqueous solution for a total recovery period of 24 hours. The positive (X-rays), negative (nutrient solution), and drug control (3% drug solution) groups were maintained in each of the three series of repeated experiments. Flower buds of the treated and control groups were fixed in aceto-alcohol (1:3 ratio) in preparation for slides to score MCN frequencies in the early tetrads of the meiotic pollen mother cells. The mean MCN frequencies (MCN/100 tetrads +/- SE) of the positive control (irradiated) was 26.68 +/- 2.49; the negative control was 2.93 +/- 0.50; the PM solution control was 2.06 +/- 0.39, and the 0.35 Gy X-ray plus 6% PM drug treated was 18.76 +/- 1.69. A 45% reduction in chromosome damage was observed. Antimutagenic effects were relatively decreased at lower concentrations of PM. This antimutagenic effect could be attributed to the antioxidant action of PM, enhancement of DNA repair, or the radical elimination from the irradiated plant cells.