Clonorchis sinensis is a liver fluke which is the most prevalent helminth of humans in Korea. The better diagnostic measure of clonorchiasis is required for its nationwide control program. The present study observed antigenic bands of C. sinensis and reacting immunoglobulins in serum of infected residents. Adult C. sinensis were recovered from experimentally infected rabbits and soluble crude extract of the worms was used as the antigen after supplementation of E-64, a cysteine proteinase inhibitor. SDS-PAGE of the crude antigen resolved more than 20 protein bands between 200 and 14 kDa. The sera of infected humans collected at an endemic village showed specific IgG and IgE antibodies but little IgM and IgA antibodies. The protein bands of 94, 80, 72, 68, 52, 47, 43, 37, 34, and 28-25 kDa strongly reacted with serum Ig(GMA) or IgG antibody and 64, 62, 52, 47, 44, 34, 28, and 26 kDa bands reacted with serum IgE antibody. However, the 94, 80, 72, 68, 64, 62, 52, 47, and 40 kDa bands of C. sinensis antigen were found non-specific. The protein bands of 43, 34, and 28-25 kDa of C. sinesis are primary target molecules of further analysis.