pH-Responsive near-infrared (NIR) cyanine dyes were encapsulated in self-assemblies consisting of anionic, cationic, and neutral amphiphiles in phosphate buffered saline. Self-assemblies of the neutral surfactant, poly(ethylene glycol)tocopherol conjugate, could efficiently encapsulate the dyes without loss of pH responsiveness over hours. pH-Responsive dyes encapsulated in self-assemblies sensitively responded to acidifying treatment, along with a substantial increase in the NIR absorption and emission.