Background: As miR-155 influences a wide spectrum of inflammatory mediators, the study of this miRNA may suggest a new insight over the cancer development mechanisms. This is why the investigation of the miR-155 expression may reveal a potential relation between inflammation and gastrointestinal cancer. The aim of the current study is to assess the miR-155 expression levels in patients with Crohn__ampersandsignrsquo;s disease (CD) and ulcerative colitis (UC). Materials and Methods: The expression of miR-155 was studied in 70 consecutive patients with a confirmed diagnosis of IBD: 35 with CD and 35 with UC and 30 healthy controls. Disease activity was evaluated by the clinical symptoms, biochemical inflammatory parameters (CRP, FCP) and validated indices for evaluating IBD activity (CDAI for CD, Montreal Classification, and partial Mayo score for UC). 25(OH)D serum concentrations were measured by a commercial paramagnetic particle chemiluminescent immunoassay for the quantitative determination of total 25 - hydroxyvitamin D [25(OH) vitamin D] levels use on Access 2 Immunoassay Systems. Serum expression of miR-155 by reverse transcriptase, a real-time quantitative polymerase chain reaction (RT-qPCR), was tested in all. Results: The analysis of the results showed that the circulating miR-155 was increased in Crohn-colitis (3.51__ampersandsignplusmn;5.22) and extensive UC (2.86__ampersandsignplusmn;5.44). Levels of CDAI above 150 were a risk factor for detection of increased miR-155 expression levels (OR=10, 91 (1.194-99,688); p=0.017). An increased miR-155 expression was detected in patients, treated with corticosteroids (5.20__ampersandsignplusmn;8.91 for UC and 3.39__ampersandsignplusmn;3.10 for CD). There was an inverse proportional moderate correlation with the levels of FCP (r= -0.344 :p__ampersandsignlt;0.05). Vitamin D deficiency (25(OH)D) led to a 1.24 higher risk for increased serum level of miR-155. Conclusions: The increased expression of miR-155 in patients with IBD is seen in disease localization in the colon, persistent inflammation, severe disease activity, vitamin D deficiency and treatment with corticosteroids.