Supramolecular nanogel, a physically crosslinked nanosize hydrogel, spontaneously self-assembles in aqueous solution via secondary interactions and is thus of great interest in nanomedicine as a drug carrier. We developed a versatile method for supramolecular nanogel self-assembled by electrostatic interaction between positive surfactant micelles and negative polypeptides. Core-shell-like structures of supramolecular nanogels provide stable hydrophobic pockets that prevent simple diffusion of hydrophobic guest molecules, resulting in high encapsulation stability. The size of the supramolecular nanogels can be systematically controlled by varying the size of the surfactant micelles. Furthermore, noncovalently encapsulated dye molecules can be released in response to matrix metalloproteinases highly overexpressed in tumor tissues, potentially providing tumor-triggered targeting.