While its antioxidant and anti-inflammatory nutrients offer protection to the entire digestive tract, celery may offer special benefits to the stomach. Celery contains polysaccharides that help keep the digestive system healthy. Polysaccharides are pectin-based antioxidants with anti-inflammatory benefits. Some recent research suggests that the antioxidants in celery could also help improve stomach lining and reduce the risk of gastric ulcers. 

Reference:

Al-Howiriny, T., et al., (2010). Gastric antiulcer, antisecretory and cytoprotective properties of celery (Apium graveolens) in rats. Pharmaceutical Biology, vol. 48, iss. 7, 786 – 793.