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Objectives: We aimed to identify dynamic CT features that can be used for prediction of local recurrence of hepatocellular carcinoma (HCC) after proton beam therapy (PBT). Methods: We retrospectively retrieved CT scans of patients with PBT-treated HCC, taken between January 2004 and December 2016. 17 recurrent lesions and 34 non-recurrent lesions were retrieved. The attenuation difference between irradiated tumor and irradiated parenchyma (ADHCC-IP) was compared in the two groups by using the Mann–Whitney U test. Cut-off value of ADHCC-IP was estimated by using the Youden index. Results: The follow-up time after PBT initiation ranged from 374 to 2402 days (median, 1069 days) in recurrent lesions, and 418 to 2923 days (median, 1091.5 days) in non-recurrent lesions (p = 0.892). The time until appearance of local recurrence after PBT initiation ranged from 189 to 2270 days (median, 497 days). ADHCC-IP of recurrent lesions [mean, −21.8 Hounsfield units (HU); from −95 to −31 HU] was significantly greater than that of non-recurrent lesions (mean, −51.7 HU; from −117 to −12 HU) at 1–2 years in portal venous phase (p = 0.039). 5-year local tumor control rates were 0.93 and 0.56 in lesions with ADHCC-IP at 1–2 years in PVP < −55 and ≥ −55 HU, respectively. Conclusion: The attenuation difference between irradiated HCC and irradiated liver parenchyma in portal venous phase at 1-2 years after PBT can predict long-term local recurrence of HCC after treatment. Advances in knowledge: We identified a cut-off value for contrast enhancement of HCC after PBT that could predict future local recurrence.