Rationale: Synchronous gastric carcinoma and hepatocellular carcinoma (HCC) is rare. It is hard to distinguish synchronous HCC from metastatic liver cancer in this condition. The treatment and prognosis is quite different for synchronous HCC of gastric carcinoma and liver metastasis of gastric carcinoma. Patient concerns: A 68-year-old man with a chief complaint of epigastric pain for 1 year, accompanied by reflux and belching. The patient was diagnosed with gastric carcinoma (cT4NxM0) and laparoscopy-assisted radical distal gastrectomy was performed. This was followed by chemotherapy of FOLFOX regimen. However, a liver nodule growth was observed after postoperative systemic treatment. Diagnosis: The initial diagnosis was liver metastasis of gastric carcinoma. However after hepatectomy of segment VI and VII as well as thrombectomy of right hepatic vein, histology revealed intermediate to poor differentiated HCC. Hence this case was diagnosed as synchronous gastric carcinoma and HCC. Interventions: A preventive transcatheter arterial chemoembolization (TACE) was conducted at 4 weeks after hepatectomy. Another FOLFOX regimen was suggested, but was refused by the patient. Outcomes: The patient survived without tumor recurrence for 9 months after the second surgery. Lessons: Synchronous HCC should be routinely distinguished from gastric carcinoma liver metastasis, especially for patients with hepatitis B virus (HBV) infection. The FOLFOX4 regimen for treating gastric carcinoma liver metastasis may have inhibited the progression of primary HCC in this case. This patient with HCC benefited from liver resection, inspite of hepatic vein tumor thrombosis.