Aim: Crohn's disease (CD) is a chronic inflammatory disease of the gastrointestinal system. Regarding its pathogenesis, it is known that transmural inflammation develops in the bowel. In recent years, it has been considered that bowel damage occurs as a consequence of an imbalance between oxidative stress and ischaemia and antioxidant capacity. Bilirubin is the metabolic product that develops as a result of heme destruction. In oxidative stress, blood bilirubin levels increase in correlation with the intensity of ischaemia. The aim of our study was to evaluate the potential of bilirubin as a serum factor to be a marker of disease activity of CD. Material and Method: Thirty patients diagnosed with active CD and 66 healthy control subjects were involved in the study. Clinical activity was determined using the Crohn's Disease Activity Index (CDAI). Serum bilirubin levels of active disease and remission periods were compared with the control group. Results: When total bilirubin values were examined, the bilirubin level among Crohn's disease patients was significantly increased compared to the control group (p < 0.05). The total bilirubin value exhibited significant alteration during the remission period (p < 0.05). Discussion: Our study showed that serum bilirubin was increased in active CD patients compared to controls.