In Bombyx mori, protein components of larval haemolymph differ qualitatively and quantitatively between two sexes. Female larvae are characterized by significantly higher concentration of total protein and presence of FL components (larval female protein). Present paper deals with haemolymph protein compositions in sex-mosaic larvae. Genetic mosaic strain having a dominant larval marking gene translocated on the W-chromosome, T(W ; 3)Ze, was used as material. Female larvae manifest narrow black bands on anterior portion of each segment, whereas males are characterized by normal white color. Sex-mosaic individuals can easily be detected by the co-manifestation of “Zebra” (femaleness) and normal (maleness) markings on the integument tissue. 1) Sex-mosaic larvae showed remarkable variations in the total concentration of haemolymph protein, amounts of FL fraction varied as well among them. 2) There was no correlation between the ratio of female and male regions on the integument and the degree of female-specificities expressed on the protein compositions of haemolymph. 3) Correlation coefficient between the total protein concentration and the percentage of FL component was less positively significant in mosaics as compared with the values obtained in normals. 4) Development of gonads was scarcely recognizable in a considerable number of sex-masaic individuals. Mosaic individuals which successfully produced eggs were shown to satisfy either or both conditions of @total concentration of haemolymph protein and ②relative amount of FL protein were comparably high with the values in females. It was, however, also evident that these are neccessary but not sufficient conditions for mosaic individuals to lead themselves to egg formation. From the results mentioned above, it was inferred that inconsistent degrees of the sexuality might be brought about by the uneven distribution of female and male cells among tissues and organs acting on different sex-related characters.