Background/Aim: The aim of the present study was to investigate the efficacy of an ethanolic extract of gamboge (EEG), a traditional Chinese medicine (TCM), both in vitro on colon cancer cells and in vivo in an orthotopic mouse model of human colon cancer. Materials and Methods: The in vitro cytotoxicity of EEG on colon cancer cells was determined with the CCK8 proliferation assay and the Annexin V-PE/7-AAD apoptosis assay. Efficacy of EEG in vivo was evaluated in an orthotopic mouse model of human colon cancer implated with the green fluorescent protein-expressing human colon cancer cell line SW480-GFP. The tumor-bearing mice were treated with vehicle (0.2 ml/dose normal saline, po, daily), irinotecan (50 mg/kg/dose, ip, twice a week), 5-FU (15 mg/kg/dose, ip, every other day) as positive controls or EEG at doses of 12.5, 25 and 50 mg/kg/dose, po, daily. Real-time fluorescence imaging was performed to determine tumor inhibition in each treated group compared to the untreated controls. The protein expression of β-catenin, MMP-7, cyclin D1 and E-cadherin in the tumors was analyzed by immunohistochemistry. Results: EEG significantly induced proliferation inhibition and apoptosis of SW480 colon cancer cells in vitro in a dose-dependent manner. Tumor growth in the colon-cancer orthotopic model was significantly inhibited by irinotecan, 5-FU and all three doses of EEG. The efficacy of EEG was comparable to irinotecan and 5-FU. Irinotecan, 5-FU and 50 mg/kg EEG significantly decreased the protein expression of β-catenin and MMP-7. Cyclin D1 expression was decreased and E-cadherin expression was increased by irinotecan, 5-FU and all three doses of EEG. Conclusion: The present study demonstrates anti-tumor efficacy of EEG on colon cancer both in vitro and in vivo through inducing proliferation inhibition and apoptosis of SW480 colon cancer cells and inhibiting tumor growth, respectively. EEG exerts anti-tumor activity at least partly via down-regulation of the Wnt/β-catenin signaling pathway.