Phellinus linteus has traditionally been used as a medicinal mushroom in Oriental countries. Bioactive phytochemicals from the fruiting body of P. linteus were investigated using the on-line HPLC-DPPH system. The system was used to separate 10 antioxidants: protocatechuic acid (1) protocatechualdehyde, (2) caffeic acid (3), ellagic acid (4), hispidin (5), davalliallactone (6), interfungins A (7), hypholomine B (8), inoscavin A (9), and methyldavallialactone (10). Of these, compounds 6 and 7 showed the strongest inhibitory effect against the DPPH radical and superoxide anion radical-scavenging capacity. On comparison with quercetin ($IC_{50}$, $44.0;{mu}M$), the $IC_{50}$ value of compounds 6 and 7 for DPPH radical-scavenging capacity were $19.6;{mu}M$ and $18.5;{mu}M$. Moreover, the antioxidative capacity of compound 6 at 40mM was 2.95 nmol Trolox equivalents per mg dry wt. These results indicated that hispidin dimers such as hispidin with hispidin or hispolon had a stronger effect on radical-scavenging capacity than hispidin itself.