Background Biomarkers predicting the response to the anticancer treatment and prognosis in patients with advanced hepatocellular carcinoma (HCC) are required. Recently, high mobility group box 1 (HMGB1) was reported to promote HCC progression and be associated with poor prognosis for patients with HCC. The purpose of this study was to assess serum HMGB1 concentrations before and during sorafenib treatment or hepatic arterial infusion chemotherapy (HAIC) and to explore the ability of serum HMGB1 concentrations to predict prognosis. Methods Serum HMGB1 concentrations were measured in 71 and 72 patients with advanced HCC treated with sorafenib and HAIC, respectively, to assess their usefulness for prediction of the response to the treatment and prognosis. Results Multivariate analysis identified high HMGB1 at 4 weeks (P = 0.001), high a-fetoprotein (AFP) at baseline (P = 0.025), tumor liver occupying rate (P = 0.009) and modified RECIST (mRECIST, P \ 0.0001) as independent Kazuhiko Masuda and Atsushi Ono are the co-first authors.The original version of this article was revised: An article note about co-first authorship was added and the second sentence in the subheading ''Results'' under the ''Abstract'' section was corrected. predictors of poor overall survival in sorafenib treatment. High HMGB1 at 4 weeks (P = 0.025), vascular invasion to the hepatic vein (Vv) (P = 0.009), mRECIST (P \ 0.0001) and Child-Pugh B (P = 0.004) were identified as independent predictors of poor overall survival in HAIC treatment. The concentrations of HMGB1 at baseline and 4 weeks were not correlated with conventional tumor markers and progressive disease assessed by mRECIST at 8 weeks.Conclusions These results suggest that serum HMGB1 at 4 weeks after the start of treatment might be a useful biomarker with added value to the conventional tumor marker and radiologic responses to predict poor overall survival in patients with advanced HCC treated with sorafenib or HAIC.