Novel dendritic triblock co-oligomer (14G2A3) consisting of ester dendrons and aniline oligomer was synthesized and found to self-assemble into fibrils in THF. Studies reveal that the formation of the fibrils originates from both of the amphiphilic interactions between the ester dendrons and oligoaniline, as well as the intermolecular pi-pi stacking among oligoanilines. The shape effect of dendrons on molecular packing was comparatively analyzed with packing parameter against its linear analogous compound. At the same time, the driving forces that dominate the final aggregating state of the block oligomer were separately investigated using the bulky-group protecting method, which allows release of the intermolecular pi-pi stacking of oligoaniline in a controlled manner. Results show that both the introduction of dendrons and the intermolecular pi-pi stacking will increase the packing parameter of the block oligomer and, consequently, cause the selfassembly morphology to evolve step by step from micelles to vesicles and finally to fibrils. The fibrils can form complexes with SWNTs to increase solubility in THF. The effective fluorescence quenching accompanied also opens a gate for the block co-oligomer to have potential applications in organic electronic devices.