In this article, we report the formation of assembly of Au nanoparticles (NPs) of different sizes in the presence of 𝑝-aminoacetanilide. Citrate stabilized spherical Au NPs assembled into a linear array, the extent of which depended on the concentration of 𝑝-aminoacetanilide in the medium. Higher concentrations led not only to the formation of longer assemblies but also branched ones. In addition, substantial fusion of NPs was observed at higher concentrations. UV-Vis spectra showed the appearance of a second peak at higher wavelength - the position of which shifted to the red with increasing concentration of 𝑝-aminoacetanilide. Interestingly, the second peak could not only be influenced by the concentration of 𝑝-aminoacetanilide but also by choosing different sizes of the spherical NPs at the initial stages. For example, when the particles were larger the shift could be observed at higher wavelengths than those starting with smaller particles. The present method allows organization of NPs into linear arrays based on the molecular properties of the `assembler’ i.e. 𝑝-aminoacetanilide. Also, the optical properties of the assembled NPs could be tuned with the choice of suitable sizes of the assembling NPs.