Morphology evolution in complexes of amphiphilic block copolymers poly(styrene)-b-poly(acrylic acid) (PS-b-PAA) and poly(styrene)-b-poly(ethylene oxide) (PS-b-PEO) in the presence of polyaniline (PANI) in aqueous solution is reported. Transmission electron microscopy, atomic force microscopy, and dynamic light scattering techniques were used to study the morphologies at various PANI contents [aniline]/[acrylic acid] ([ANI]/[AA]) ranging from 0.1 to 0.7. The interpolyelectrolyte complex formed between PAA and PANI plays a key role in the morphology transformation. Spherical micelles formed from pure block copolymers were transformed into large compound vesicles upon increasing PANI concentration due to internal block copolymer segregation. In addition to varying PANI content, the kinetic pathway of nanoparticle formation was controlled through different water addition methods and was critical in the formation of multigeometry nanoparticles.