Penthorum chinense Pursh, widely distributed in eastern Asia, has long been used in China for both food and medicine due to its various bioactivities. The aim of this study was to isolate its active compounds with antioxidant and antihepatocarcinoma properties. P. chinense was extracted with 95% ethanol, 70% ethanol, and water, respectively, and then the 70% ethanol extract was re-extracted, resulting in petroleum ether, ethyl acetate, n-butanol, and water fractions, subsequently. Results showed that the antioxidant and antihepatocarcinoma activities of ethanol extracts were stronger than those of aqueous extract, and the ethyl acetate fraction of 70% ethanol extract showed the highest activities. Four compounds, β-sitosterol, quercetin, pinocembrin-7-O-[3-O-galloyl-4″,6″-hexahydroxydiphenoyl]-β-glucose (PGHG), and thonningianins A (Th A), were isolated from the ethyl acetate fraction and identified by UV, MS, and NMR spectroscopic analysis. Th A was isolated from P. chinense for the first time. PGHG and Th A exhibited higher antioxidant and antihepatocarcinoma activities than did other isolated parts of P. chinense . The antihepatocarcinoma activity of Th A was much higher than that of positive control (5-fluorouracil). PGHG and Th A were suggested to be the active chemical compositions responsible for potent antioxidant and antihepatocarcinoma properties of P. chinense , which are worthy of further study.