Heat-processed Asian ginseng roots (Panax ginseng C.A. Meyer), also known as "red ginseng" in Asia, are reported to have more bioactivity than the no-processed white ginseng roots. Therefore, American fresh ginseng roots (Panax quinquefolius L.) were processed to the red ginseng and examined changes in bioactivity during heating process. The fresh America ginseng roots were steamed at 100 degrees C for 30, 60, 90 and 120 min, and their bioactivities were examined by analyzing the content of ginsenosides and total phenolics, and measuring DPPH and superoxide radical scavenging acivity and their protective effects on V79-4 cells viability and lipid peroxidation. The heating treatment proportionally increased total ginsenosides (4.97%, w/w) content compared with white ginseng (3.27%) and total phenolics from 444.5 mg GAE/100 g to 489.6-574.2 mg GAE/100 g. The antioxidant activity also increased from 285 mg/100 g (vitamin C equivalent) to 353-487 mg/100 g. Heated ginseng showed high levels of DPPH radical scavenging activity (59.5-88.5%) and the high level of superoxide radical scavenging activity (44.2-90.9%). The heated ginseng protected cell viability against H2O2-induced oxidative damage, and enhanced the activities of superoxide dismutase and catalase by dose dependently in V79-4 cells.