A highly versatile approach to fabricate functional gold nanoparticle (AuNP)-polymer hybrids is demonstrated by employing sulfonated block copolymers. The 35 nm sized ionic domain of the sulfonated poly(styrene-block-methylbutylene) (SnMBm) copolymers can be utilized as a nanoreactor where the Au ions can be selectively sequestered and reduced to AuNPs using a simple photochemical method. The size of the AuNPs can be adjusted in fine-steps from 2.0 +/- 0.3 to 3.9 +/- 0.5 nm by changing the sulfonation levels of the SnMBm copolymers. Remarkably, significantly improved methanol oxidation properties are achieved with the hybrid materials owing to the ion conductingSO3H groups and the interconnected network of AuNPs confined within the self-assembled microstructures, which provides electronic conductivity.