To a better understanding of tick embryogenesis, the Boophilus microplus egg proteins degradation was studied. A complex profile mainly represented by 19.1, 138.3, 128.5, 114.9, 103.1, 83.0, 71.7 and 45.4 kDa peptides was showed, using polyacrylamide gel electrophoresis in denaturating conditions. Changes in protein composition began at third day of egg incubation suggesting the beginning of embryogenesis. Egg proteolysis occured at low pH and cysteine proteinase inhibitors avoid degradation at different times of incubation preferentially at advanced embryogenesis. The cysteine-dependant acid proteolysis was represented by the presence of cathepsin B and L-like activity. A chymotrypsin like activity also appeared in the eggs at late embryogenesis and its value also reached a miximum with hatching.