Objective:To explore expression and prognostic value of oncostatin M(OSM)in endometrial cancer and to analyze relationship between OSM expression and immune cell infiltration in endometrial cancer tissues.Methods:OSM expression in pan-can-cer was analyzed by TIMER database,OSM expression in endometrial cancer and normal tissues was compared,and survival analysis for patients with different OSM expression was performed;relationship between OSM expression and immune cell infiltration was analyzed by TIMER and TISIDB,and ssGSEA algorithm was used to calculate difference in abundance of immune cell infiltration in samples with different OSM expression;GSEA software was applied to perform enrichment analysis;clinical tissue samples were collected for validation.Results:OSM expression was higher in endometrial cancer tissues than that in normal endometrial tissues(P=4.1e-28),and endometrial cancer patients with high OSM expression had prolonged recurrence-free survival(RFS)(P=0.004 8).OSM expression was positively correlated with abundance of immune cell infiltration and genetic markers of immune cells(P<0.05).OSM was mainly enriched in immune-related signaling pathways.OSM expression was higher in endometrial cancer tissues than normal and atypical hyperplastic tissues(P=0.016 9).Proportions of immune cell markers CD4,CD8,and CD68 were increased in tumor tissues with high OSM expression(all P<0.05),which were positively correlated with OSM expression.Conclusion:OSM is highly expressed in endometrial cancer tissues and correlated with prognosis;OSM expression is positively correlated with immune cell infiltration level and can be used as a biomarker for immunotherapy and prognosis.