It is shown that gelatinous solutions in cyclohexane of a Zn complex of a long-chain triester of meso-tetrakis[p-carboxy]phenyl porphyrin (ZnP3) are made up of rodlike assemblies. The presence of both Zn atom and carboxylic function, reinforcing the usual pi-pi interactions, is determinant for the aggregation. The carboxylic groups in ZnP3 tetramers are associated in the central core of ca. 60 Angstrom diameter rods. J-type lateral aggregation is characterized by a typical Soret exciton absorption. Small-angle neutron scattering profiles are analyzed to detail the network composition as a function of concentration of ZnP3 or of an end-capping molecule such as pyridine. A model of supramolecular organization in the rods is proposed with four ZnP3 molecules laterally associated per section and with a slipped arrangement of consecutive layers in tilted columnar rods.