Abstract:This paper reports the research on the determination of indican in Polygonum tinctorium with dual-wavelength TLC scan method. This microquantitative method is quicker, and more direct than the previous gravimetric method. With this method, the contents of indican in various growth periods of Polygonum tinctorium have been determined. The result shows that the highest contents appear in the period August～September, thus providing a guideline for better utilizing this plant and appraising its quality.