Stimulus-responsive hydrogels are promising as a platform for controlled drug release and regenerative medicine. We describe a polymer grafted with self-assembling triphenylalanine (FFF) peptides that shows pH responsive hydrogelation. Protonation of the carboxylate groups of the C-termini of FFF induce self-assembly of the peptide moiety, leading to hydrogelation via physical crosslinking. In situ imaging directly visualizes the porous network structure and the hydrogelation process, which are distinct from those of a hydrogel comprising a short peptide-type hydrogelator.