Gold nanoparticles (Au NPs) have been synthesized using simple thermolysis, whether from the mesophase or from toluene solutions, of mesogenic alkynyl-isocyanide gold complexes [Au(C C-C6H4-CmH2m+1) (C N-C6H4-O-CnH2n+1)]. The thermal decomposition from the mesophase is much slower than from solution and produces a more heterogeneous size distribution of the nanoparticles. Working in toluene solution, the size of nanoparticles can be modulated from similar to 2 to similar to 20 nm by tuning the chain lengths of the ligands present in the precursor. Different experimental conditions have been analyzed to reveal the processes governing the formation of the gold nanoparticles. Experiments on the effect of adding ligands or bubbling oxygen support that the thermal decomposition is a bimolecular process that starts by decoordination of the isocyanide ligand, producing an oxidative coupling of the akynyl group to [R-C C-C C-R] and reduction of gold(I) to gold(0) as nanoparticles. The nanopartides obtained behave as a catalyst in the oxidation of isocyanide (CNR) to isocyanate (OCNR), which in turn cooperates to catalyze the decomposition.