We report here a case of a 21-year-old Japanese woman suffering from severe acute liver injury due to hepatitis C virus (HCV) infection in the third trimester of her first pregnancy. When a second-generation antibody reactivity to HCV had not yet appeared, HCV RNA was detected in her serum using a polymerase chain reaction. Subsequent natural interferon-alpha therapy played a key role in the recovery from severe hepatic injury, and the disappearance of HCV RNA in her serum. Consequently, HCV RNA has not been detected for over 17 months after the cessation of interferon administration. On the other hand HCV RNA was not detected in her cord or the baby serum. Therefore, maternal transmission of HCV was not evidenced. This is a rare case in which a severe form of acute hepatitis C was successfully treated with natural interferon-alpha, and no indication of a maternal transmission of HCV in acute hepatitis C could be demonstrated with polymerase chain reaction analysis.