Ordering and orientation of conjugated polymers (CPs) into well-defined supramolecular structures render the exploration of new properties of the assemblies. However, the fabrication of an asymmetric structure such as a bowl-shaped nanostructure by self-assembly from rigid CPs is still a major challenge because of their extremely rigid molecular backbones. Here, amphiphilic diblock copolymer [polystyrene-b-poly(acrylic acid), PS-b-PAA] and small molecule (phenylboronic acid, PBA) were employed as additives into the CPs to guide the formation of fully water-soluble bowl-shaped vesicles driven by the synergy of pi-pi stacking interactions, hydrophobic interactions, and hydrogen-bonding interactions between the three components. The size of the openings and interior holes of the nanobowls can be precisely controlled by varying the amount of PBA. This assembly strategy may open an avenue for the construction of a series of CP-based bowl-shaped vesicles. Furthermore, the water-soluble fluorescent nanobowls may act as a useful platform for drug delivery and chemical sensing applications.