Abstract: The biological activity of chrysophanol on the development of Sphaerotheca fuliginea Poll. and the uptake translocation of chrysophanol in cucumber leaves were determined by spraying method.The results showed that chrysophanol has high toxicity against S.fuliginea ,powdery mildew colonies on the infected leaves were brown and dead at 2 days after being treated with 200 mg/L chrysophanol.Morphological investigation by scanning electron microscopy showed that chrysophanol affected fungal survival,caused distortion and malformation of hyphae and conidiophores,and conidia collapsed.The efficacy of chrysophanol in controlling cucumber powdery mildew,remained 84.83% 20 days after foliages spraying with chrysophanol at 100 mg/L on cucumber cotyledons,which was similar to that of 50% sulfur SC at 500 mg/L.Moreover,chrysophanol showed certain cross-layer and little transverse effect in cucumber plants,but no acropetal and basipetal uptake translocation effect.