To evaluate the histological effect of arterial embolization chemotherapy (AEC) for the metastatic liver tumors from colorectal cancer, 5 lesions were examined in 4 patients who were treated with surgery after AEC. In addition, to compare the histological changes of the metastatic liver tumors, we histologically examined 7 lesions in 5 patients who were treated with surgery alone as a historical control. For the patients with AEC, anti-cancer agents and lipiodol were administered by selected hepatic arterial infusion with fragments of sponzel. In a group of AEC, all metastatic liver tumors were detected after resection of the primary tumors. The range of tumor size in these lesions was from 2.5 to 4.2 cm in diameter. Otherwise, in a group of non-AEC, the size of tumors ranged from 2 to 5 cm in diameter. In angiography, tumor stainings were detected in 2 lesions, and in all lesions no accumulation of lipiodol was detected by CT scan. The overall response rate at the surgery was 7 to 33% (average 23%) in a group of AEC. In addition, in 2 lesions, about 60% of the lesions were necrotic tissues, and more than 90% of the tumor lesions in 3 lesions were histologically necrosis. Within these lesions, encapsulation of the metastatic tumors was observed in 3 lesions. Otherwise, in a group of non-AEC, 50-70% of the tumor lesions were histologically detected as necrosis, and in one lesion, encapsulation was observed. These evidences suggest the histological effect of AEC may be evaluated when more than 70% of tumor necrosis in lesions is observed. In conclusion, the treatment was effective in 3 cases and not effective in one case.