Polyclonal antibodies made against 86kDa (86k), 80kDa (80k) and 54kDa (54k) vitellins of Oxya japonica japonica are used for Western blotting. Anti-80k vitellin antibody is cross-reacted with a 95kDa (95k) vitellin. While 95k vitellin is present both in the female hemolymph and in the oocyte, 80k vitellin is detected only in the oocyte and the laid egg. In the growing oocytes, as 95k vitellin is faded out gradually, 80k vitellin is accumulated increasingly, indicating postendocytic processing of 95k vitellin brings 80k vitellin. Further conforming the hypothesis, partial digestion of 95k vitellin with pepsin and $alpha$-chymotrypsin makes several protein bands of molecular weight around 80 kDa. Thus, the 95k vitellin may have a cleavage site(s) to produce 80k vitellin which forms fairly stable tertiary structure. In the reduced condition (20mM glutathion), both 95k and 80k vitellins were digested throughly by endogenous proteinase at pH 4. Both 86k and 54k vitellins, respectively, show no apparent molecular weight changes in the growing oocyte and in the hemolymph.