Portal vein embolization (PVE) is expected to have an adjuvant effect on the treatment of human liver tumors with transcatheter hepatic arterial embolization (TAE). In this experimental study, PVE was tried using two kinds of embolic materials, steel coils (coils) and absolute ethanol (ethanol). The aim of this article is to compare the effectiveness between the two methods. Five dogs and 12 dogs were treated with coils and ethanol, respectively. The second order portal branches were embolized. Embolization effects of each embolic material on the hepatic vessels and the liver parenchyma were studied angiographically and histologically. PVE with coils achieved immediate occlusion of the embolized vessels in all dogs. Unexpectedly, unembolized vessels were also constricted and/or obstructed in 4 of 5 dogs during a 4-week follow-up period. Histological examination showed no hepatic necrosis in all dogs. By contrast, in the dogs treated with ethanol, venous occlusion was achieved immediately after embolization with ethanol of 0.4 mL/kg or more. The embolized vessels remained occluded and no obstruction of unembolized vessels was observed until 4 weeks after embolization. Hepatic necrosis was observed in the segments where portal veins were occluded. The degree of parenchymal damage was proportional to the injected ethanol dose. Judging from these results, ethanol is likely to be more suitable than coils as an embolic material for PVE. PVE with coils is often dangerous because unembolized vessels might be occluded unexpectedly. For the clinical use of PVE with ethanol, the appropriate dose of injection should be investigated.