This study was carried out to investigate the changes of ginsenoside compositions and antioxidant activity of fresh ginseng induced by thermal processing at different temperatures (25, 100, 121, and $150^{circ}C$), pressure (0.1, 10, 20, and 30 MPa), and soaking solvents (water and ethanol). The levels of ginsenosides were similar trend with the pressure of 0.1-30 MPa, while there were significantly differences in heated ginseng with heating temperature and soaking solvent. When water and ethanol was used, the ginsenoside compositions significantly changed at 100 and $121^{circ}C$, respectively, and it was rapidly decreased at $150^{circ}C$. After heating, the level of 3 ginsenosides (Re, Rf, and Rg1) decreased and that of 5 other ginsenosides [Rb1, Rb2, Rb3, Rc, and Rg2(S)] increased up to $121^{circ}C$ compare to raw ginseng. Ginsenoside F2, F4, Rg2(R), Rk3, Rh4, Rg3(S), Rg3(R), Rk1, and Rg5, which was absent in raw ginseng, was detected in heated ginseng. Especially, ginsenoside Rg3(S), Rg3(R), Rk1, and Rg5 were remarkably produced after thermal processing. After heating, the phenolic compounds (1.43-11.62 mg/g), 50% inhibition concentration ($IC_{50}$) value (1.48-3.11 mg/g), and ABTS radical scavenging activity (0.66-9.09 mg AA eq/g) of heated ginseng were increased.