PURPOSE: To determine the factors predisposing to the intratumoral gas formation after TACE in the treatment of HCC. MATERIALS AND METHODS: A total of 176 pathologically or clinically proven patients with HCC on whom CT scan had been performed in 2 weeks to 3months after TACE were reviewed. The patients were classified in two groups; intratumoral gas-forming group(n=18) and non-gas forming group(n=158). Chi-square (X2) test was applied to analyze the factors influencing to gas formation. The radiological factors studied were the morphologic type and location of HCC, presence or absence of tumor capsule on CT, the degree of tumor vascularities, presence or absence of portal vein thrombosis, presence or absence of arterioportal shunt, and TACE catheterization method on angiegraphic examination and the duration of post-TAE fever. RESULT: Intratumoral gas foramtion after TACE occurred significantly in tumors with peripheral location or capsule on CT tumors with less vascularity or peripheral arterioportal shunt on angiegraphic examination, and TACE with selective catheterization method(p<0.05). But the morphologic types of HCC and presence of main portal vein thrombosis were not significantly different between the two groups (p>0.05). The average duration of fever sustained after TACE was longer in gas-forming group than those in non-gas forming group (p<0.05). CONCLUSION: TACE of HCC with weak collaterals or with peripherd prevent recanalization from collaterals has tendency to intratumoral gas form-his and prolonged fever duration.