Hepatoid adenocarcinoma (HAC) is a group of neoplasms with features resembling hepatocellular carcinoma. The stomach is the most commonly affected organ among the reported primary sites. We report the case of a 28-year-old man with chronic hepatitis B and a complaint of abdominal distension. The patient was examined by PET-CT and magnetic resonance imaging (MRI), which showed diffuse thickening of the peritoneum and omentum but no mass was found in the liver. Pathological examination of a biopsy of the omental nodules was consistent with moderately differentiated hepatocellular carcinoma (HCC); thus, a diagnosis of HAC of the peritoneum and omentum was established. The patient received a chemotherapy regimen consisting of oxaliplatin and capecitabine and gained remarkable effects as the AFP level dropped significantly, and the tumour nearly disappeared. When the patient shifted to the standard multikinase inhibitors, Sorafenib or Lenvatinib, both treatments were ineffective. HAC is a heterogeneous group of prognostically unfavourable tumours mimicking the histological appearance of HCC, and the treatment outcomes are still unclear.