Background. The aim of this study was to determine the potential prognostic roles of the perioperative interleukin-6 (IL-6) level and its dynamic changes in patients with hepatocellular carcinoma (HCC) undergoing transarterial chemoembolization (TACE). Materials and Methods. Sixty patients with hepatitis B virus-associated HCC receiving TACE were enrolled in the study. Serum IL-6 levels were determined at baseline and 1 day after TACE by immunoassay. Response to TACE was evaluated after a 4-6-week interval. Factors associated with tumor response were analyzed by univariate and multivariate analysis in a Cox regression model. Receiver operating characteristic (ROC) curve analysis was performed to assess the predictive performance of the included variables on tumor response in patients with HCC undergoing TACE. Results. The serum IL-6 level was significantly elevated 1 day after TACE. Patients in the low postintervention IL-6 level group had a high probability of achieving an objective response (OR) (66.7% vs. 18.8%, p = .021). Post-TACE IL-6 level (≤12.7 pg/mL) and post-/pre-TACE neutrophils ratio (>2.47) were independently correlated with OR after TACE. ROC curve analysis showed that a combined index based on those two factors exhibited optimal predictive power of tumor response among all the included variables (area under the curve = 0.740, 95% confidence interval: 0.601-0.879). Additionally, high post-TACE plasma IL-6 level was associated with maximum tumor size, vascular invasion, post-TACE aspartate aminotransferase, and Barcelona Clinic Liver Cancer stage. Conclusion. Our study suggests that the post-treatment serum IL-6 level, rather than pretreatment or dynamic changes of IL-6, serves as a powerful predictor for tumor response. These findings provide evidence to help discriminate between patients who will particularly benefit from TACE and those who require more personalized therapeutic regimens and rigorous surveillance. The Oncologist 2019;24:e1489-e1495 Implications for Practice: Transarterial chemoembolization (TACE) is a major therapeutic regimen for advanced hepatocellular carcinoma. Thus, identification of early practical markers of tumor response to TACE is of high importance. This study indicated that the post-treatment serum interleukin-6 (IL-6) level, rather than the pretreatment or dynamic changes of IL-6, serves as a powerful predictor for tumor response. A combined index based on the post-TACE IL-6 level and post-/pre-TACE neutrophils ratio is optimal for predetermining an objective response after TACE, which may be helpful in guiding individualized treatments and surveillance.