Abstract: Whole sera of sex-reversing individuals as well as of females and males in Monopterus were analysed respectively through polyacrylamide gel (7%, pH 8.8) disc electrophoresis. Resuits show that the electrophoretic bands of serum proteins in both sexes of Monopterus increase with gonad development. The electrophoretic patterns obtained by 7% gel showed 10—11 serum protein bands in female Monopterus (gonadal stage Ⅲ-Ⅳ); while those in male were 11—14 (gonadal stages Ⅰ-Ⅳ). However the number of serum proteins of sex-reversing Monopterus has even more distinct increase, serum protein showing more than 20 bands in the electrophoreric gel. The serum albumin of inter sexual Monopterus had 4 bands in the electrophoretic gel, being the same as that of the female. The number of electrophoretic bands of serum liporoteins in females, located the negative pole, was identical with that of the male individuals, having 5 bands. In intersexual fish the r-globulin and B-globulin proteins of medial molecular size were distinctly different from those of the female and the male individuals, the paper showing 11—12 bands in the former.For this reason, the authors consider that the increase of the larger molecular sized serum globulins is somewhat correlated to the sex-reversing process in Monopterus.