The authors report a case of idiopathic portal hypertension (IPH), which showed interesting RI accumulation on Single Photon Emission CT (SPECT) images, with Tc-99m galactosyl human serum albumin (GSA) scintigraphy. Accumulation of Tc-99m GSA was decreased in the periphery of the liver where strong enhancement was revealed only in the arterial phase on dynamic CT. These findings imply that portal flow is decreased in the periphery of the liver where arterial flow is dominant. It was thought that secondary reduced activity of GSA due to a decrease in portal flow results in reduced radioactivity in the periphery of the liver in IPH. This interesting accumulation of Tc-99m GSA may be one of the sign of IPH.