The preparation of hydrogels and stable emulsions is important in the formulation of many functional nanostructured soft materials. We investigate the multifunctional self-assembly and bioactivity properties of a novel surfactantlike peptide (SLP) that shows antimicrobial activity, is able to form hydrogels without pH adjustment, and is able to stabilize oil-in-water emulsions. Furthermore, we demonstrate on-demand de-emulsification in response to the protease enzyme elastase. We show that SLP

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... Ala) 9 -Arg (A 9 R) forms β-sheet fibers above a critical aggregation concentration and that water-in-oil emulsions are stabilized by a coating of β-sheet fibers around the emulsion droplets. Furthermore, we demonstrate enzymeresponsive de-emulsification, which has potential in the development of responsive release systems. The peptide shows selective antimicrobial activity against Gram-negative pathogens including Pseudomonas aeruginosa, which causes serious infections. Our results highlight the utility of SLPs in the stabilization of oil/water emulsions and the potential for these to be used to formulate antimicrobial peptide emulsions which are additionally responsive to protease. The peptide A 9 R has pronounced antibacterial activity against clinically challenging pathogens, and its ability to form β-sheet fibers plays a key role in its diverse structural properties, ranging from hydrogel formation to emulsion stabilization.