We observed the changes of unstriped muscle of portal vein and superior mesenteric artery in rabbits infected with schistosomiasis in different stages with Masson trichrome stain. The results showed compensatory hypertrophy and hyperplasia of unstriped muscle of internal and medial layer of portal vein and superior mesenteric artery. It is concluded that the portal system is volume vessel as well as resistance vessel, which can counteract the intrahepatic resistance, maintaining the liver blood flow supply. The hyperdynamic circulation of viscera contributes to elevation of constrict power of the superior mesenteric artery, resulting in compensatory hypertrophy and hyperplasia of the unstriped muscle.