We report the case of a boy with chronic septic granulomatosis (CSG) who presented with a marked gastric antrum narrowing which was evaluated by MRI after oral intake of magnetic contrast particles, and after gadolinium i.v. administration. In particular, a mammillated aspect of the gastric wall in the antral region was seen. Follow-up by MRI clearly showed the gradual resolution of hyperemic wall thickness, after medical management. The antral stenosis resolved after 3 months. Magnetic resonance imaging provides detailed evaluation of gastric wall inflammation in course of CSG.