The compatible miracidium is able to inhibit without stimulate the immune defense mechanism of its snail. So, snail failed to recognize it as foreign body. A level of antigenic similarity must be present between the miracidia and its natural snail intermediate host (IH). The present study investigated the level of compatibility or difference in molecular structures between miracidia and their specific snails IH using protein fractionation and western blot (EITB). Specific anti-snail rat hyper immune sera (RHIS) were obtained by rat vaccination. This RHIS was reacted versus different miracidial antigens (Ag) to determine the compatibility level between any miracidium and the target snail Ag using EITB. The results showed five polypeptides bands at molecular weight (MW) of 100kda, 60kda, 50kda, 45kda & 35-38kda, common between S. mansoni miracidium Ag and B. alexandrina feet Ag. Three fractions at MW of 58kda, 38-42kda & 22-24kda were recognized in fractionated F. gigantica miracidium versus anti-L. natalensis Ab. Six polypeptide bands at MW of 48-50kda, 38-40kda, 30kda, 25 kda, 22.5kda & 15kda were recognized between E. revolutum miracidia and P. acuta fractionated feet Ag. There was no polypeptide bands between any miracidium and snail other than its specific one.