Background: Sea anemone peptides are promising tools for understanding physiological functions of ion channels. Results: A new peptide, Ugr 9-1, was isolated from the sea anemone venom and was shown to inhibit the acid-sensing ion channel 3 (ASIC3) channel. Conclusion: Ugr 9-1 affects the ASIC3 channel, produces analgesic effects, and has a unique spatial structure and mechanism of action. Significance: Ugr 9-1 represents a novel structural fold of natural short peptides modulating neuronal channels. © 2013 by The American Society for Biochemistry and Molecular Biology, Inc.