Abstract: A TLC-densitometric method is proposed for the quantitative determination of sesquiterpene lactone in Loranthus parasiticus(L.) Merr. parasiting on Coriaria sinica Maxim and in the seeds of Coriaria sinica Maxim. The standard curve is linear in the range of 1～8 μg of lactone. The method is shown to be rapid and reproducible. The procedure is as follows:Weigh accurately 2g of pulverized sample of crude drug and reflux with 15 ml ethanol on a waterbath for 1 h. Take 10 ml of the extract and evaporate to dryness. After dissolving the residue in 2 ml of absolute alcohol, 0.4 g of polyamide(90 mesh) is added. After drying, the mixture is transferred to the top of a column(170 × 12mm) packed with poiyamide(60 mesh) for purification and eluted with 30% ethanol. After concentrating the eluent by vacuum distillation, the residue is dissolved in 1.0 ml of methanol. 6 μl of the solution and standard solution are spotted alternately on a silica gel plate which is then developed with cyclohexane-ethyl acetate(1: 1). After drying, the plate is sprayed with an alcoholic solution of 3% vanillinsulfuric acid and heated at 80℃ for 15 min. The spots of the lactones are determined by a TLC scanner. The recoveries of coriamyrtin(A), tutin(B) and coriatin(C) are 96.3±5.1, 97.7±4.3 and 97.4±4.6%, respectively.