Defining early reliable surrogate end points for survival in patients with hepatocellular carcinoma (HCC) after conventional transarterial chemoembolization (cTACE) is of great value. To evaluate the association between sustained response duration (SRD) and overall survival (OS) after cTACE for intermediate HCC. This multicenter cohort study enrolled 2403 consecutive patients in China with naive intermediate HCC between June 1, 2000, and December 31, 2008, as the primary cohort, and 331 consecutive patients with intermediate naive HCC between January 1, 2011, to June 30, 2012, as the validation cohort. All patients received cTACE as an initial treatment. Initial response and best response were defined as the radiological response after first cTACE or best radiological response after 2 or more sessions of cTACE, respectively. Responders were those who experienced complete response or partial response. Sustained response duration was defined as the time between the date when complete response, partial response, or stable disease was achieved and the date progressive disease occurred after cTACE. Response was evaluated by modified Response Evaluation Criteria in Solid Tumors. Information about patients in the study was collected from January 1, 2018, to March 31, 2018, and analysis of these data was performed in April 2018. Overall survival. A total of 2734 total patients (2499 of 2734 [91.4%] male; median [range] age, 56.5 [18-75] years) were included in the analysis. In the primary cohort, SRD of 6 months or more was found to have the strongest association with 5-year OS after cTACE among different durations of sustained response. Patients with SRD of 6 months or more (387 of 430 male; median [range] age, 57 [18-75] years) had the longest median (range) OS (67.7 [64.8-72.1] months), followed by initial responders (760 of 874 male; median [range] age, 56 [18-75] years; median [range] OS, 55.8 [55.0-57.7] months) and best responders (939 of 1032 male; median [range] age, 57 [18-75] years; median [range] OS, 53.2 [52.2-54.6] months). Response duration of 6 months or more was found to be an independent prognostic factor for OS (hazard ratio, 0.145; 95% CI, 0.124-0.170; P < .001). The significance of SRD as a factor associated with OS was confirmed in the validation cohort. Sustained response duration of 6 months or more was associated with OS and may serve as an early surrogate end point after cTACE for intermediate HCC.