Polyethyleneglycol-block-poly(N,N'-diethylaminoethyl methacrylate) (PEG-b-PDEAEM) copolymers were used as nanoreactors for the preparation of gold nanoparticles (AuNPs) in aqueous and alcoholic medium. These copolymers were synthesized changing the size of the PDEAEM block by using reversible addition-fragmentation chain transfer (RAFT) polymerization as demonstrated by nuclear magnetic resonance and gel permeation chromatography measurements. The PEG-b-PDEAEM block copolymers were dispersed in water to form aggregates with sizes around 100 nm, depending on the lengths of the PDEAEM segment as well as the pH of the solution. The corresponding unimers were evident when these same copolymers were dissolved in alcohol or tetrahydrofuran medium showing hydrodynamic diameters (D-h) between 4 and 10 nm. The aggregates and unimers were used as nanoreactors for the synthesis of AuNPs and were characterized using UV-Vis spectroscopy, dynamic light scattering and transmission electron microscopy. The AuNPs had a sphere-like shape with a diameter from 7 +/- 1.7 to 34 +/- 6 nm depending on the type of aggregate/unimer used in the synthesis. Nevertheless, when very large aggregates were used, AuNPs with different morphologies were observed.