A synthesis strategy for a hyperbranched sulfonated polydiphenylamine was developed. First, a hyperbranched polyvinylbenzoxylamine (H-PVBPA) was prepared by controlled atom transfer radical copolymerization of an amino-protected vinylbenzoxylamine (4-VBPA-(BOC)-B-t) and 4-chloromethyl styrene followed by deprotection. Second, H-PVBPA was reacted with sodium diphenylamine sulfonate under acidic conditions to generate hyperbranched sulfonated polydiphenylamine (H-PSDA). The H-PSDA exhibited conductivities of 3.7 x 10(-2) and 1.2 x 10(-2) S/cm in HCl-doped and self-doped states, respectively. The microstructure of H-PSDA in aqueous solutions was found to be sensitive to the pH. In the dedoped state (at pH greater than or equal to 7), AFM identified nanoscale particles of uniform size around 40 nm. The self-doped H-PSDA aggregated at pH = 7 via intermolecular doping interaction, generating large and irregular particles (>200 nm). When the pH was decreased below 5, the aggregates could be dispersed as smaller particles of about 120 nm because of the replacement of the intermolecular self-doping by the external-doping interaction caused by the small molecules of HCl.