To evaluate the value of serum interleukin 6 (sIL-6) for the prediction of therapeutic effect and adverse reaction after transcatheter arterial embolization (TAE), sIL-6 was measured before and after angiography or TAE in 18 patients (three after angiography and 15 after TAE for hepatocellular carcinoma). The three patients with only angiography showed no elevation of sIL-6, while a significant increase was observed after TAE in the 15 hepatocellular carcinoma patients. The sIL-6 levels of patients with a partial response to TAE were higher at 48-72 hours after the procedure than those of patients with no response (P = 0.045), and the sIL-6 levels of patients who showed adverse reactions were higher at 6-24 h than those of patients without adverse reactions (P = 0.019). sIL-6 level at 48-72 h after TAE reflects the efficacy of TAE, whereas the level at 6-24 h after TAE is related to the severity of adverse reactions. Therefore, sIL-6 may be a useful indicator for prediction of the therapeutic effect of TAE as well as adverse reactions.