Objective: To investigate the effect of Opuntia humifusa aqueous extract on gastric ulcers. Methods: An ethanol-induced model was used to examine the protective effect of Opuntia humifusa against gastric ulcers. The gastric ulcer index was evaluated via clinical observation and image analysis. Various inflammatory indicators were determined by RT-PCR and Western blotting assays. Results: The gastric ulcer index was reduced to 8% in the group treated with Opuntia humifusa aqueous extract compared with that in the control group. RT-PCR analysis revealed that MUC5AC expression was reduced to 39% in the control group compared with the non-treated group, whereas the omeprazole and Opuntia humifusa aqueous extract-treated groups increased the expression to 95% and 79%, respectively. Moreover, the expressions of various cytokines including TNF-α, IL-1β, and IL-6 were increased in the control group, while decreasing in Opuntia humifusa aqueous extract-treated group. Opuntia humifusa aqueous extract also suppressed the expressions of iNOS, COX-2, and its transcription factor NF-κB and increased mucus content considerably as compared to the control group. Conclusions: These results suggest that Opuntia humifusa aqueous extract is suitable as an alternative remedy for gastric ulcer treatment.