Background: Few studies have investigated the efficacy of comprehensive therapy, including immunotherapy, for gastric cancer with synchronous liver metastases (GCLM). We compared the effect between immunochemotherapy and chemotherapy alone as a conversion therapy on the oncological outcomes of patients with GCLM. Methods: Clinicopathological data of 100 patients with GCLM from February 2017 to October 2021 from our institution were retrospectively analyzed. The patients were divided into immunochemotherapy (n=33) and chemotherapy alone groups (n=67). Results: The baseline clinicopathological data did not significantly differ between two groups. The immunochemotherapy group had higher overall response (59.4% vs. 44.0%, P=0.029) and disease control rates (71.9% vs. 49.2%, P=0.036) than the chemotherapy group. The immunochemotherapy group showed better tumor regression in gastric mass, metastasis lymph nodes, and liver lesion than did the chemotherapy group. Ten (30.3%) patients in the immunochemotherapy group and thirteen (19.4%) in the chemotherapy group underwent surgery after conversion therapy. However, the difference was not significant. The overall survival (OS) and progression-free survival (PFS) rates were better in the immunochemotherapy group than in the chemotherapy group. Treatment-related adverse events occurred in 24 (72.7%) and 47 (70.1%) patients in the immunochemotherapy and chemotherapy groups, respectively. Conclusions: As a conversion therapy for GCLM, immunotherapy yielded better primary and metastatic tumor regression and survival benefit, with no increase in adverse events than did chemotherapy.