Background　Oxidative　stress,　immune　response,　and　inflammation　play　an　important　role　in　the　occurrence　and　progression　of　gastric　cancer　(GC).　This　study　is　to　develop　a　novel　prognostic　oxidative　stress-immune-inflammation　score　(POSII　score)　and　to　explore　the　clinical　value　of　the　novel　nomograms　incorporating　this　factor　in　survival　and　recurrence　risk.　Methods　This　study　included　3612　GC　patients　who　underwent　radical　gastrectomy　at　three　tertiary　hospitals　from　2009　to　2020.　One　hospital　formed　the　training　and　internal　validation　cohorts,　while　the　other　two　constituted　the　external　validation　cohort.　Twelve　hematological　markers　were　collected　and　analyzed　to　develop　the　POSII　score　via　LASSO　regression.　Two　online　calculators　were　developed　and　validated.　Results　The　POSII　score　categorized　patients　into　low　and　high　POSII　groups,　with　the　low　POSII　group　showing　significantly　improved　5-year　overall　survival　(OS)　and　disease-free　survival　(DFS)　rates,　as　well　as　a　markedly　reduced　risk　of　recurrence　(all　P　＜　0.05).　Multivariate　COX　regression　showed　that　the　POSII　score　was　an　independent　prognostic　factor.　Based　on　the　POSII　score,　two　nomograms　(OS:　AUC　=　0.837;　DFS:　AUC　=　0.834,　respectively)　for　individualized　prognostic　prediction　were　constructed.　To　enhance　clinical　usability,　we　further　developed　two　user-friendly　online　calculators.　The　high-risk　group　had　an　earlier,　more　persistent　peak　of　recurrence　and　a　high　incidence　of　multiple　recurrence　patterns.　Conclusion　Two　novel　online　calculators　based　on　the　POSII　score　can　be　used　as　reliable　tools　for　predicting　survival　and　recurrence　after　radical　gastrectomy.　Our　findings　provide　new　insights　into　the　role　of　cancer-related　immune　dysregulation,　inflammation,　and　oxidative　stress　imbalances.