In this study, we investigated the inhibitory activities on gastritis and gastric ulcer using liriodendrin which is a constituent isolated from Kalopanax pictus. To elucidate its abilities to prevent gastric injury, we measured the quantity of prostaglandin $E_2$ ($PGE_2$) as the protective factor, and we assessed inhibition of activities related to excessive gastric acid be notorious for aggressive factor and inhibition of Helicobacter pylori (H. pylori) colonization known as a cause of chronic gastritis, gastric ulcer, and gastric cancer. Liriodendrin exhibited higher $PGE_2$ level than rebamipide used as a positive control group at the dose of $500{mu}M$. It was also exhibited acid-neutralizing capacity (10.3%) and $H^+/K^+$-ATPase inhibition of 42.6% ($500{mu}M$). In pylorus-ligated rats, liriodendrin showed lower volume of gastric juice ($4.38{pm}2.14ml$), slightly higher pH ($1.53{pm}0.41$), and smaller total acid output ($0.47{pm}0.3mEq/4hrs$) than the control group. Furthermore liriodendrin inhibited colonization of H. pylori effectively. In vivo test, liriodendrin significantly inhibited both of HCl/EtOH-induced gastritis (46.9 %) and indomethacin-induced gastric ulcer (46.1%). From these results, we suggest that liriodendrin could be utilized for the treatment and/or protection of gastritis and gastric ulcer.