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 surfactant-like 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 (Ala)(9)-Arg (A(9)R) forms beta-sheet fibers above a critical aggregation concentration and that water-in-oil emulsions are stabilized by a coating of beta-sheet fibers around the emulsion droplets. Furthermore, we demonstrate enzyme-responsive 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 beta-sheet fibers plays a key role in its diverse structural properties, ranging from hydrogel formation to emulsion stabilization.