Two strains of endophytic fungi, Penicillium melinii Yuan-25 and Penicillium janthinellum Yuan-27, with strong anti-Pyricularia oryzae activity, were obtained from the roots of Panax ginseng. Based on bioactivity-oriented isolation, a new benzaldehyde derivative, ginsenocin (1), together with six known compounds, methyl 2,4-dihydroxy-3,5,6-trimethylbenzoate (2), 3,4,5-trimethyl-1,2-benzenediol (3), penicillic acid (4), mannitol (5), ergosterol (6), and ergosterol peroxide (7), were separated from the EtOAc extract of Yuan-25 culture, while brefeldin A (8) was isolated as the major constituent from the EtOAc extract of Yuan-27 culture. The chemical structures were determined based on spectroscopic methods. All the isolated compounds 1-8 were evaluated for their cytotoxicity against six human cancer cell lines. Brefeldin A (8) was the most cytotoxic constituent against all the tested cell lines with IC50 values < 0.12 mu g/ml, while ginsenocin (1) and penicillic acid (4) also exhibited potent cytotoxicity with IC50 values ranging from 0.49 to 7.46 mu g/ml. Our results suggest that endophytic fungi isolated from P. ginseng are a promising natural source of potential anticancer agents.