Objective:To examine the effect of the aqueous extract of Ligustrum robustum on tumor growth in vitro and in vivo and explore the possible molecular mechanisms.Methods:In in vitro study,cell viabilities of human cervical carcinoma cells (HeLa),human breast cancer cells (MCF-7),human prostate cancer cells (PC-3),human hepatoma cells (7721) and human colon carcinoma cells (SW480) were evaluated with cell counting kit-8.For L.robustum-treated Hela cells,early or late apoptosis were evaluated by annexin V/PI staining.Mitochondrial membrane potential was measured by staining cells with JC-1.Apoptosis was monitored by nuclear morphology based on chromatin condensation and fragmentation by 4\',6-diamidino-2-phenylinole (DAPI) staining.Caspase-3 and-8 activity levels were measured by a colorimetric assay.In vivo,to evaluate the possible mechanism of L.robustum-mediated antitumor effect,nude mouse xenograft study was also conducted.Results:In in vitro study,L.robustum was found to be toxic to HeLa,MCF-7,PC-3,7721,SW480,with an half maximal inhibitory concentration value of 2-5 mg/mL (P＜0.05).Moreover,externalization of phosphatidylserine,loss of mitochondrial membrane potential,DNA fragmentation and activation of caspase-3 and-8 were detected in L.robustumtreated Heia cells.Using a nude mouse model bearing Hela xenografts,we found that L.robustum reduced tumor volume and tumor weight (P＜0.05),but had no effect on body weight and histological damage of important organs.Intraperitoneal injection of L.robustum caused a significant reduction in serum aspartate transaminase and alanine transaminase levels (P＜0.05).Furthermore,cleaved caspase-3-positive and terminal nucleotidyl transferase-mediated nick end labeling (TUNEL)-positive cells were observed in L.robustum-treated tumor tissues.Conclusions:L.robustum inhibits tumor cell growth both in vitro and in vivo by inducing apoptosis in a caspasedependent way without apparent hepatic toxicity and histological damage,which may offer partial scientific support for the ethnopharmacological claims of L.robustum as a herbal tea for its antitumor activity.