Background: Previously, two phase III clinical trials of immune checkpoint inhibitors (ICI) failed to meet their primary endpoints, leading to doubts regarding the clinical activity of ICI monotherapy in patients with aHCC. Here, we comprehensively examined clinicopathological factors and estimated their association with survival outcomes in aHCC patients treated with nivolumab. Methods: A total of 261 eligible patients from 5 high-volume centers who were treated with nivolumab between June 9, 2012 and March 14, 2018 and had measurable diseases were reviewed. We reviewed more than 80 clinicopathological factors and categorized them into 6 areas: 1) demographics (n = 16); 2) baseline laboratory values (n = 19); 3) tumor burden (n = 12); 4) previous treatment (n = 12); 5) treatment response (n = 5); 6) toxicity profiles (n = 18). Their association with survival outcomes were evaluated, and organ-specific response evaluation, adapted from RECIST 1.1, was conducted. Results: Of the 261 patients, 218 (84%) had extrahepatic spread. The median follow-up time was 4.5 months. The median progression-free survival (PFS) and overall survival (OS) were 2.3 months (95% CI, 1.8-2.8) and 6.3 months (95% CI, 5.0-8.2). Objective response rate was 15%. Subgroup analyses revealed that compensated liver function (Child-Pugh score A5/6), surrogate markers for low tumor burden (low AFP, low PIVKA, and low LDH level), inflammatory markers (low C-reactive protein [CRP], low erythrocyte sedimentation rate [ESR], low neutrophil-to-lymphocyte ratio [NLR], high lymphocyte-to-monocyte ratio [LMR]), and low intrahepatic tumor burden were significantly associated with longer OS. A total of 456 individual lesions (liver, n = 249; lung, n = 124; lymph node, n = 35; others such as boner soft tissues, n = 48) were examined. Organ-specific response rates (hepatic tumor, 9%; lung, 25%; lymph node, 37%; others metastasis, 15%) were different, of which intrahepatic tumor was the least responsive organ to ICI treatment in aHCC. Conclusions: Underlying liver function, the tumor extent and burden, and the degree of plasma lymphocytes are crucial for determining tumor response to ICI in aHCC. Antitumor immune response to ICI differs in an organ-specific manner. The hepatic tumors of HCC may be less responsive to nivolumab than extrahepatic lesions.