In this paper, a silica-gel-modified carbon paste electrode (Si-gel/ CPE) was used to determine the anti-cancer drug emodin by anodic stripping differential pulse voltammetry (ASDPV). The effects of the silica-gel content, the pH of the supporting electrolyte, and the scan rate on the oxidation current of emodin were investigated. The oxidation currents of emodin obtained from ASDPV measurements were linearly correlated with the concentration in the range of 5.0 x 10(-9) to 300.0 x 10(-9) mol L-1. The limit of detection was determined to be 1.5 x 10(-9) mol L-1. The current method was successfully applied to determine emodin in a knotweed root sample, with recovery rate of 92.5% to 98.3%.