Abstract: Herbicidal components of Cephalotaxus sinensis against Amaranthus retroflexus were isolated by bioassay-guided separation. The main active components were alkaloids in chloroform partition derived from the ethanol extract. Drupacine, cephalotaxine and 11-hydroxycephalotaxine were isolated from the chloroform partition first by silica gel column chromatography(CC) and then by aluminum oxide CC respectively, and identified by IR, MS ,1H NMR. The herbicidal activity of drupacine and 11-hydroxycephalotaxine were much higher than cephalotaxine. The inhibitory rates of drupacine and 11-hydroxycephalotaxine to the growth of root and stem of Amaranthus retroflexus were nearly or more than 80% at 1 mg/mL concentration.