Here we report the ultrafast photolysis of fluorescein dyes in the presence of polymer nanomicelles, which were formed by the direct dispersion of amphiphilic hyperbranched poly(ether amine) (hPEA) in aqueous solution. The detailed investigation revealed that the hPEA nanomicelles exhibit a very strong interaction with fluorescein dyes and can encapsulate them as nanoreactors in aqueous solution. Thus, the concentration of both dyes and amine groups increases in the microenvironment, which leads to the fast photobleaching of dyes and the generation of free radicals. This study greatly impacts the applications of fluorescein dyes in various fields, especially as visible photoinitiators in photocuring coatings and adhesives.