A 71-year-old man with unresectable liver metastasis from colon cancer was treated by hepatic intraarterial infusion of low dose 5-FU (250 mg/body/day). The tumor measured 18 cm by ultrasonography and has reduced gradually to five cm during three years. Both serum CEA and CA 19-9 levels were as high as 49.9 ng/ml and 5,500 U/ml respectively, before treatment, but normalized. This case suggested that this hepatic intraarterial infusion of low-dose 5-FU might be effective to treat unresectable liver metastasis, especially with portal tumor thrombosis.