The proteinases responsible for the degradation of yolk proteins in the eggs of Cyprinus carpio were studied. It was proofed that were endogenous proteinases in the oocytes. The optimum pH of the proteinases to the yolk proteins was about 3. The activities of the proteinases could be inhibited by E-64 and pepstatin, which suggested the proteinases belonged to the cysteine peoteinase family and aspartic proteinase family. The proteinases could hydrolyze the bovine hemoglobin at pH4. There was one major kind of protein in the yolk proteins, which was estimated as 110 kDa by SDS-PAGE.This rpotein was the major endosubstrate of the proteinases.