Gastric cancer is a malignant tumor with a fifth position amid all cancers and its mortality rate is third, globally. But the frequency varies in several parts of the world. In India, amongst men it is the fifth most common cancer and in women it is in seventh position. The objective was to study the clinical significance of serum CA125 and its relation to PD in cases of gastric cancer.Materials and Methods: An observational study with cross-sectional design was conducted by the Department of Pathology, Indira Gandhi Institute of Medical Science, Patna, Bihar, India from May 2021 to April 2022 were studied. The study included samples from 25 patients during this duration. Approval from the Institutional Ethics Committee and written informed consent from the patients was taken.All the gastrectomy specimens were sent for gross examination, staging and histopathology. The paraffin embedded tissue blocks were subsequently stained for H&E.Microsoft excel 2016 and Statistical Package for the Social Sciences (SPSS) version 18 (SPSS, Inc. Chicago, IL, USA) was used for data analysis.Results:TNM staging was done. T3 stage (16, 53.3%) comprised the major bulk of the cases followed by T2 (7, 23.3%), T4 (5, 16.7%) and T1 (2, 6.7%). Likewise, N2 nodal staging (18, 60%) was leading followed by N0 (9, 30%), N1 (2, 6.7%) and N3 (1, 3.3%). Distal metastasis was noted among 36.7% (11 cases) of the cases with liver as the most common site of metastasis followed by PD, left supraclavicular lymph node, and multiple metastases. Majority of the cases were stage IIIA (17, 56.7%) and stage IV (12, 40%).Conclusion: Early detection of peritoneal disease will help the clinicians to stratify the treatment of gastric cancers and to decide