Well-defined stimuli-responsive mono and dual fullerene (C-60) end-capped poly( acrylic acid)s (PAA-C-60 and C-60-PAA-C-60) were synthesized by reacting C-60 with well-defined mono and dual azide end-functionalized poly(tert-butyl acrylate) s, followed by hydrolysis. The aggregation behaviors of these C-60 end-capped polymers in aqueous solution were examined using potentiometric and conductometric titrations and static and dynamic light scattering as well as transmission electron microscopy (TEM). Both PAA-C-60 and C-60-PAA-C-60 show pH-responsive and water-soluble properties at high pH. Both polymers self-assemble to form large compound micelles (LCMs) in aqueous solutions. The LCMs of PAA-C-60 exist as "compact aggregates", whereas the LCMs of C-60-PAA-C-60 possess a "core-shell" structure with a larger size and aggregation number. The micelles for both polymers swell upon neutralization, where the Rh of PAA-C-60 micelles increases from similar to 44 to similar to 102 nm and the Rh of C-60-PAA-C-60 aggregates varies from similar to 89 to similar to 128 nm with increasing degree of neutralization. The lower swelling of the dual end-capped C-60-PAA-C-60 system is related to its higher C-60 content, which enhances the interpolymer chain hydrophobic association that restrains the swelling of micellar aggregates.