Purpose The aim of this study was to investigate the diagnostic efficacy and image quality of magnetic resonance enterography (MRE) using oral mannitol solution for the evaluation Crohn disease (CD). Materials and methods We retrospectively evaluated MRE examinations of 153 patients with an assumed or definitive diagnosis of CD. There were 65 men and 88 women, with a mean age of 35.7 years (range: 6–73 years). MRE findings of the patients were compared to histopathologic results obtained by surgery-fiberoptic endoscopy. The sensitivity, specificity and diagnostic efficacy rate were calculated. Additionally, image quality of MRE was evaluated using a four-point scale (1 = excellent, 4 = poor/non-diagnostic). Results Sensitivity, specificity and diagnostic efficacy were 92.5%, 93% and 92.8%, respectively. Six patients had false-positive and five patients had false-negative findings. Three falsely positive patients had ulcerative colitis and three had non-specific terminal ileitis. A total of 765 small bowel segments were analyzed; 475 (62%) had an image quality score of 1 and 15 (2%), an image quality score of 4. Conclusion MRE using oral mannitol solution provides excellent image quality for MRE and has high degrees of diagnostic efficacy in CD patients.