Inflammation of gastrointestinal (GI) tract remained a challenge for radiologist. Image findings are usually nonspecific and subtle in much modality. Since the diagnosis of inflammatory bowel disease (IBD) is not simply made, clinical presentation, endoscopic findings, image features, and pathology can be complimentary. In the literature, computed tomography (CT) depicted "fat halo sign" of GI tract was once regarded as specific findings for IBD. However, some authors found this sign can be a normal variant in obese patient with non-distended GI tract. In this article, we report a young, underweighted man, who had pathologically proved chronic gastritis and "fat halo sign" on CT, and successfully treated as Crohn's disease.