In this paper, we have studied the supramolecular photocatalytic performance of porphyrin-based nanofibers and nanospheres in terms of photodegradation of rhodamine B (RhB) pollutant under visible light irradiation, wherein interesting morphology-dependent photocatalytic activity has been achieved. We have demonstrated that nanofibers, which are synthesized by means of surfactant-assisted self-assembly of zinc 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (ZnTPyP), display distinct photocatalytic activity for the photodegradation of RhB molecules, where the bleaching reaction could be repeatedly operated 8 times. When the spherical nanostructures are employed, however, only negligible photocatalytic activity could be observed. The electron paramagnetic resonance investigations have revealed that singlet oxygen species are generated when spherical ZnTPyP nanostructures are employed, whereas hydroxyl radical species are produced in the nanofiber system. An electron transfer process is suggested to be responsible for the photocatalytic performance of the fibrous nanoassemblies. It is revealed that the monomeric state of ZnTPyP in the spherical nanostructures disfavors the electron transfer process, resulting in negligible photocatalytic activity. On the contrary, the formation of J-aggregates in the nanofibers facilitates the electron transfer process, resulting in distinct photocatalytic performance. The investigation suggests that an artificial supramolecular nanoantenna system based on nanostructured porphyrin assemblies could be achieved by tuning the molecular arrangement of the nanoassemblies.