Gastric ulcer is a global health concern nowadays. Adinandra nitida, known as Shibi tea, is a flavonoid-rich plant found in South China. A. nitida possesses many healthy properties, such as antioxidation and reducing blood pressure. However, its effects on gastric ulcer have not been investigated. This study aimed to investigate the effects of the Shibi tea water extract (STE) and its main flavonoid camellianin A (CA) in hydrochloric acid (HCl) and ethanol (EtOH)-induced acute gastric ulcer in mice. Administration of CA and STE for continuous two days after stimulation by HCl/EtOH significantly attenuated the deterioration of gastric mucosal damage by lowering the gross gastric mucosal index, histopathological injury index, the oxidative stress, the expression of the inflammatory cytokines TNF-α and IL-6, and the expression of inflammatory mediators iNOS and COX-2. Western blotting and immunohistochemistry analysis showed that CA and STE regulated the inflammatory signaling pathway protein levels of IκB-α and NF-κB. Taken together, our study verified that CA and STE have antioxidative and anti-inflammatory effects in gastric ulcer mice. We propose that A. nitida should be developed as natural functional food for acute gastric ulcer patients base on the gastroprotective effects of STE and its main flavonoid CA.