Background: Inflammatory bowel diseases (IBD) consist of Crohn's disease (CD) and ulcerative colitis (UC). They are characterized by a chronic relapsing and remitting disease course that results in intestinal symptoms but also frequently in extra-intestinal manifestations. Among potential targets and biomarkers, oncostatin M (OSM) has gained a lot of interest. OSM is a pleiotropic cytokine produced by activated T cells, monocytes, macrophages, and neutrophils. It is considered proinflammatory given its ability to promote leukocyte recruitment. Objective: This study aimed to assess the value of oncostatin M as a potential biomarker in diagnosis, follow up and prediction of response to treatment of inflammatory bowel disease. Patients and Methods: The study included30 patients with IBD (15 with ulcerative colitis and 15 with Crohn's disease) from Outpatient Clinic of Gastroenterology Department of Ain Shams University Hospital as a study group. 30 healthy subjects were enrolled in this study as a control group. Results: The mean Oncostatin M in IBD cases before treatment was 120.13 Pg/ml while after treatment was 91.17 Pg/ml with high significant difference. There was high statistical correlation in between fecal calprotectin level after treatment and oncostatin M after treatment. ROC curve for oncostatin level in diagnosis of IBD cases showed that the best cut off point between groups regarding the level of oncostatin was > 78.50 Pg/ml with sensitivity of 96.7%, specificity of 100%. ROC curve for oncostatin in prediction of response to treatment showed that the best cut off point between groups regarding the oncostatin level was found < 103.50 Pg/ml with sensitivity of 40%, specificity of 75% Conclusion: Oncostatin M is a promising marker for the diagnosis and follow-up of IBD patients, however it has a limited predictive performance for the prediction of the response for IBD treatment.