Abstract We study the composition effect of non‐polar organic media in cetyltrimethylammonium bromide (CTAB) reverse micelles (RMs) on the interface properties and their use as nanoreactors for gold nanoparticles (AuNPs) synthesis. We evaluate how the molecular structure of aliphatic ( n ‐hexane) and aromatic (toluene) organic solvent influences the environments and interactions at the interface of n ‐hexane/1‐butanol/CTAB and toluene/1‐butanol/CTAB RMs, as a key factor on AuNPs finals properties. Data show that the intermicellar exchange rate is affected by changing the organic solvent, and these facts influence AuNPs size, polydispersity, and morphology. FTIR and 1 H NMR results suggest that in n ‐hexane a rigid and compact micellar interface favors the formation of smaller AuNPs, while in toluene a more fluent micellar interface enhances the formation of larger and dispersed AuNPs. This specific interaction also affects the CTAB counterion (Br − ) availability at the interface, which appears to be crucial to induce anisotropy of the AuNPs obtained.