Inflammation is related to several chronic diseases, including cancer and atherosclerosis. Taxillus sutchuenensis (Lecomte) Danser is a special folk medicinal plant in Taiwan. The aim of this study was to evaluate the antioxidant, anti-inflammatory, and antiproliferative activities of the aqueous-thanol extract from T. sutchuenensis (AETS) and its fractions. TEAC, DPPH radicals, total phenolic compounds, total flavonoid content, inhibition of NO production in LPS-induced RAW264.7 cells, and inhibition of cancer cell proliferation were tested. Among all fractions, the ethyl-acetate (EA) fraction showed the highest TEAC and DPPH radical scavenging activities. The EA fraction also had the highest polyphenol and flavonoid content. The EA fractions also decreased LPS-induced NO production and the expression of iNOS and COX-2 in RAW264.7 cells. The antiproliferative activities of the aqueous/ethanol extract and fractions were studied in vitro using A549 cells, and the results were consistent with their antioxidant capacities. EA fractions had the highest antiproliferative activity with an IC(50) of 454.38 ± 1.48 μg/ml. Quercetin also had antioxidant, anti-inflammatory, and antiproliferative activities. Quercetin might be an important bioactive compound in T. sutchuenensis. The experimental data indicated that T. sutchuenensis is a potent antioxidant medicinal plant, and such efficacy may be mainly attributed to its polyphenolic compounds.