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Introduction Ultra-processed food (UPF) consumption has increased globally and has been linked to several non-communicable diseases including cancer. However, evidence regarding its association with gastric cancer (GC) remains limited and inconsistent. This systematic review aimed to evaluate the association between UPF consumption and GC risk.Methods This systematic review was conducted according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and registered in PROSPERO (CRD42024504965). PubMed, Scopus and Google Scholar were searched for studies published from January 1991 to April 2024, with an updated search in February 2025. Eligible studies were observational studies assessing the association between UPF consumption, specific UPF categories or UPF-related dietary patterns and GC risk. Two reviewers independently screened studies, extracted data and assessed methodological quality using the Joanna Briggs Institute checklist. Due to heterogeneity in exposure definitions, outcome classification and effect estimates, findings were synthesised narratively.Results Seventeen studies were included, comprising 14 case–control studies and 3 cohort studies, with a total of 276825 participants. Eight studies reported positive associations between UPF consumption and GC risk, three reported no association and six showed mixed findings depending on UPF category, population subgroup or cancer subtype. Processed meats, fried or fast foods, sugary beverages, highly processed dairy products and Western-style dietary patterns were more frequently associated with increased GC risk. However, findings varied across studies due to differences in dietary assessment methods, UPF classification, exposure categories and confounder adjustment.Conclusions The available evidence suggests a potential association between UPF consumption and GC risk, particularly for processed meats, fried foods and UPF-rich dietary patterns. However, the evidence remains inconclusive because of methodological heterogeneity and reliance on observational studies. Further prospective studies using standardised UPF classifications and validated dietary assessment tools are needed.PROSPERO registration number CRD42024504965.