Objective To study the effect of five free anthraquinones of rheum on Staphylococcus aureus. Method Total anthraquinones was extracted by pH grades extraction, and the effect on restraining bacterium was measured by bisection method. Result Emodin, aloe-emodin, rhein has the effect of restraining bacterium, chyrsophanol and physcion has not the effect of restraining bacterium. Of the effect on restraining bacterium, emodin is the best, then is aloe-emodin, rhein is the worst. Conclution Rheum has the effect of restraining bacterium.